(FORTUNE Magazine) – It is a little before 11 P.M. in Las Vegas, and despite the seductive universe of slot machines and sex, Maurice Miller is out cruising Wal-Mart parking lots. Again. "By midnight that lot will be f-u-l-l," he huffs in his Texas twang. He flicks the cigarette permanently nestled between his thick fingers and points out the window at the rows upon rows of cars. It doesn't seem as though the overflowing parking lot can be any fuller than it already is. The 16 Wal-Marts in Vegas are open 24 hours a day, seven days a week. That means Miller, 49, a self-described short, fat man with a wild salt-and-pepper beard, diamond studs in both ears, and an I-don't-take-any-crap attitude, never gets a break from one of the toughest jobs around. He is a full-time union organizer, and his mission is to convince Wal-Mart employees that they should join the UFCW (United Food and Commercial Workers). So he is always searching for workers--in parking lots and beyond--who might want to talk. Tonight he sees no likely prospects. Maybe tomorrow he'll have better luck.

Wal-Mart is the nation's largest employer, and not a single one of its 1.3 million workers ("associates" in Wal-Martese) is a union member. Changing that statistic, some union leaders argue, is the labor movement's most important challenge right now. "If we want to survive," says Stewart Acuff, organizing director of the AFL-CIO, "labor has no choice but to organize Wal-Mart." Though individual unions usually do not band together across turf lines for organizing drives, discussions are now underway across the labor community about what they call "the Wal-Mart problem." "What they do affects the standard of living across the globe," explains Acuff, referring to the retailer's ability to force competitors to move their wages and prices downward to compete. "In essence, Wal-Mart is a third-party negotiator at every bargaining table."

This may be the ultimate labor vs. company battle--a battle that the weakened labor movement desperately needs to win. For a rare inside look, FORTUNE spent ten days--the length of a union organizer's shift--shadowing people like Miller who are working on "the Wal-Mart problem." There are 12 of them, men and women living hundreds of miles from their spouses and children, slogging through days that are exhausting, lonely, and mind-numbingly boring. What's worse, even though the organizers have been camped out in Vegas for almost five years, buttonholing as many Wal-Mart associates as they possibly can, they still haven't succeeded in unionizing a single store. Despite all their dedication, they may well be fighting a battle they just can't win.

The campaign against the discount chain really started with Maurice Miller. Miller is something of a celebrity in the Wal-Mart labor movement, because he is responsible for the only modest success that the UFCW has had with the company. In 1999 he was a meat cutter at a Wal-Mart in Jacksonville, Texas; his wedding band sits on the stump of the ring finger on his left hand. That year, Miller says, Wal-Mart denied him a promotion into management that he had been promised. (A Wal-Mart spokesperson says the company does not comment on individual employment matters.) Frustrated, Miller asked his brother-in-law, an electrician in Kentucky, what he would do about it. The brother-in-law said he would file a grievance with his union.

"What do you do if you don't have a union?" Miller asked.

"You start one," his brother-in-law answered.

That night Miller sat at his computer and searched for unions. He came across the UFCW, which represents 1.4 million workers, mostly in grocery and retail stores. He signed a union card a few days later. (To unionize a workplace, 30% of workers must sign cards calling for an election held by the National Labor Relations Board, or NLRB. Unions usually won't call an election, though, unless at least half of the workers sign cards; they want to ensure a win.) Within a couple of months Miller had persuaded the rest of the meat cutters at his store to sign cards too. In February 2000 the department became the first in the chain to vote to establish a union. And with that, the labor movement had its toe in Wal-Mart.

Two weeks later Wal-Mart disbanded its meat-cutting departments nationwide. It now supplies its stores with prepackaged meat. Wal-Mart maintains that the move was in the works before the union drive. But the move galvanized the UFCW. The union decided to attack Wal-Mart in Las Vegas, which is a strong union town. In the spring of 2000 it began flying organizers there from across the country. Bill Meyer, 52, a veteran UFCW organizer who leads the Vegas campaign, arrived that spring and never left. He found the task in Vegas to be "monumental." News of what had happened to the Texas meat cutters had had a chilling effect. And Wal-Mart's culture was so strong that organizers unfamiliar with the company language and traditions were not making a dent. So in 2001 the union took the unusual step of relying almost exclusively on former Wal-Mart workers, even former Wal-Mart managers, to lead the campaign. Folks like take-no-crap Miller.

But Miller and his compatriots face formidable hurdles. For one thing, Wal-Mart is a very sophisticated adversary. According to Cornell University's office of labor research, 74% of U.S. employers currently wage moderate to extremely aggressive anti-union campaigns, Wal-Mart among them. While spokesperson Christi Gallagher maintains that the company is "pro-associate, not anti-union," Wal-Mart does everything from asking store managers to call a 24-hour hotline at the slightest sign of union activity to flying a ten-person labor team into stores to talk to employees. For another, Wal-Mart--like most retailers--has a large part-time, transient workforce; that's one reason retail has one of the lowest rates of unionization of any sector of the economy, hovering just under 5%. Many Wal-Mart employees work in Southern states where unionism isn't widely understood or embraced. And while many Wal-Mart workers undoubtedly want a union, none of them has stepped up to be the next Maurice Miller. Al Zack, the lead strategizer of the union's Wal-Mart campaign, who works from UFCW headquarters in Washington, D.C., gives this a positive spin: "All they are waiting for is for someone else to go first."

Union organizers are the foot soldiers of the labor movement. They spend their lives on the road, sleeping in aging hotels like the Frontier in Vegas, earning $35,000 to $60,000 a year (more than many Wal-Mart hourly employees make, but much less than many store managers do) and often working way past the sacred eight-hour day. In Las Vegas the UFCW's Wal-Mart organizers work ten-day shifts, then fly back to their homes in different parts of the country for four days at a time. Jon Lehman, 43, a former Wal-Mart manager, sees his wife and three children in Louisville just 72 days a year. On one flight back home, he says, "This is when I really start to miss my kids."

The organizers' days officially begin at about 9 A.M., when they huddle in Meyer's dingy suite at the Frontier for their daily strategy meeting. (Miller already looks tired. He started making calls at 6 A.M. to workers coming off the night shift or to those on the East Coast who have reached out to the union.) But most of the organizers' time is spent driving nondescript rental cars to areas far from the strip, knocking on doors where no one ever seems to be home, or cruising Wal-Mart parking lots that always seem to be full. On the road their cellphones ring constantly with calls from workers, loved ones, and one another ("Lunch at the Palms buffet?").

It frequently takes five to six hours of knocking on doors before an organizer makes it inside a single house. "It is the same thing every day," admits Miller as he leaves an unmarked brown-paper bag of union materials at the door of a worker who's not home. The union's literature, updated since the arrival of the former Wal-Mart workers, quotes Sam Walton--never mind that Walton openly disliked unions--and pleads with associates to unionize to bring their store up to the standards that "Mr. Sam" would have wanted.

The boredom can be intense. "Oh, please, something happen," organizer Gretchen Adams, 57, sighs one afternoon behind the wheel. Four years ago Adams was a store manager in Florida with a reputation for speaking up for workers, which she says did not make her a favorite with top brass. Unbeknown to her, her husband got in touch with the UFCW on her behalf, and the union sent her an e-mail at home. "I got so scared," she says. "I was convinced Wal-Mart would find out and I would lose my job." A month later, she finally responded to the e-mail; in 2001 she quit and signed on as an organizer, taking a pay cut that, she says, was "in the tens of thousands."

It's 6:30 P.M., and Adams and her partner, Mary Lou Wagoner, haven't been inside a house all day. They knock on yet another door, a gray one on the second floor of an apartment complex. Success! A slight woman in her 60s, wearing a housedress and slippers, appears. She's a Wal-Mart associate who works nights, and she invites them to sit down in her tiny kitchenette. As easy-listening jazz plays at a deafening volume, the woman spends much of the next two hours venting about her boss. "I can't take the favoritism anymore," she says softly, looking past the organizers into a small living room covered in floral prints and frilly doilies. They nod their heads in support and barely utter a word. ("Most workers just want someone to listen," Adams tells me later.)

When the associate says that her recent "eval" (Wal-Mart-speak for evaluation) was unfair, Adams asks her, "Did you get a copy of it?"

The associate's eyes get big. "You serious? I can get that?"

"You should get a copy of anything you sign," advises Adams. "Start a folder with all that paperwork."

"I can get a copy of my eval? Really," the woman repeats, still in disbelief.

By 9 P.M., tired and hungry, the organizers get up to leave. And they finally come to the point of their visit: Adams asks the associate if there are others in her department who might be ready to sign union cards. (The woman has already signed one.) The associate names a few and promises to talk with them.

It is hard to imagine Cesar Chavez, whose impassioned speeches helped unionize migrant farmers, or Wyndham Mortimer, whose massive sit-down strikes shut down assembly lines at GM, having days like this.

The UFCW used to be more in-your-face. "In the old days we'd be chanting and protesting in the parking lot," says organizer Stan Fortune. "Now we are less confrontational and more covert." They have adopted this under-the-radar approach partly because they say Wal-Mart workers are too frightened to speak to them openly and partly because they don't want Wal-Mart to know the number of union card signers at any given store. If a company knows that more than 30% of workers have signed and therefore a vote is close, says Kate Bronfenbrenner, director of labor education research at Cornell, the easiest way to prevent that from happening is to flood a store with more bodies--"packing the unit," as the tactic is known. The 30% then drops to, say, 20%--and the organizers have to recruit another 10%. Wal-Mart denies doing that.

When organizers do venture into stores, they often pose as shoppers, pushing carts and discreetly nodding to workers who have signed cards. It doesn't always work. Store managers frequently throw the organizers out. But even that is discreet. On a recent venture to a Vegas store, organizer Lehman gets out just a few hellos to workers before declaring, "We are being stalked." Since his head never seems to look anywhere but straight down the empty aisle, I'm convinced he's paranoid. But out of nowhere, one of the store's managers appears. The two exchange pleasantries the way co-workers do who have to tolerate each other: Lehman compliments the manager on losing a little weight; the manager says politely, "Thank you for noticing." Then the manager asks Lehman to leave. It is back to the car. Lehman hasn't talked to a single new face today about the union.

Some of the most fervent organizers are the newest converts--like Larry Allen, 48. Allen was an associate in a Vegas store in 2001 when Miller persuaded him to sign a union card. "The first day I walked into Wal-Mart with a union button, everything changed," says Allen. "In one day I went from being employee of the month to people not speaking to me." Last summer Wal-Mart fired Allen for solicitation; the company says that he was handing union literature to a co-worker in the store's break room. Allen denies it. The union claims that Wal-Mart fired him in order to quash an upcoming NLRB election there. (After investing 14 long months of work at the store, Miller says he had accumulated nearly enough card signers to call an election.) Wal-Mart says that's not so. The labor board is now hearing Allen's case. Meanwhile, Allen has paired up with Miller to organize full-time.

"How are you doing?" Allen says enthusiastically to every person wearing a blue Wal-Mart vest who passes him in the parking lot early one afternoon. (Miller hangs back quietly; he has cruised these parking lots so often that he recognizes the managers' cars and has already told Allen the coast is clear.) Most associates hurry past. Allen's UFCW T-shirt makes it obvious what he'd like to talk about. When he does get a nod back from one middle-aged woman, he hands her what he says is "interesting reading material." He watches her walk away, then cheers: She made it past the trash can without throwing the union pamphlet away. "Got one!" Allen exults.

It is a reminder that the organizers exist in a world where victories are subtle. Stan Fortune, 47, who was a cop before working for Wal-Mart for 14 years, spends much of his time tracking down internal company documents--such as pay scales or anti-union memos--that might strengthen the union's argument with workers. Usually workers give him the materials, sometimes anonymously. Fortune has gotten into the habit of keeping his car window cracked whenever he parks in a Wal-Mart lot: "It is amazing what [documents] people will slip inside."

To break up the document digging, once every six weeks Fortune makes the two-hour drive from Vegas to Kingman, Ariz., to speak to associates at his old store, taking in postcard views of Hoover Dam along the way. "Look at it!" he marvels as he steers the wheel with his knees so that he can drink a can of Coca-Cola mixed with peanuts. Kingman is too small to have a UFCW union hall, so Fortune usually meets workers at a local Mexican restaurant on Route 66. The waitresses, who are used to seeing him, usher him to a private room in the back. The room is loud: Bright colors are everywhere, and a train rumbles by right outside the open window. Two associates are waiting. Fortune's cellphone rings; a third associate won't be able to make it this time. The scene is a world away from Vegas, but the talk is the same: Workers want respect and better benefits; the union says it can help. "We have to get the fence sitters," Fortune tells them, referring to associates who are still iffy about signing union cards. "It is going to take patience."

Though the organizers acknowledge that five years is a long time to wage a union campaign, they don't talk about any other outcome but winning. "We know we are not going to have any immediate results," says Meyer. "But we are building a movement. Women's suffrage took decades; the civil rights movement took a century. We are looking at something similar with Wal-Mart." But some observers question how long the UFCW realistically can keep at it. Because of the grocery worker strike it waged in California from October 2003 to February 2004, the union is strapped for cash--and the Vegas effort is costing some $3 million a year. In April, UFCW strategizer Zack was debating whether to lay off one or two of the 12 Wal-Mart organizers to save money. Even if the union did have bottomless pockets, the odds of success would be long. "No one can do it [unionize Wal-Mart] alone," says Ruth Milkman, director of the institute for labor and employment at the University of California. "It needs a full-fledged multi-union effort." So far, that hasn't materialized.

In the meantime, Gretchen Adams has more doors to knock on. Stan Fortune has more documents to hunt. Maurice Miller has more parking lots to cruise. On the tenth day of the shift, they have planes to get on so that they can see their families.

And in four days it will all start again.

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