NEW YORK (CNNMoney.com) -- Bank of America stepped up the online trading wars Wednesday, offering 30 free online trades a month for customers with at least $25,000 in deposits or other accounts at the nation's No. 2 bank.

The move is the latest by the Charlotte, N.C.-based company to capitalize on its nationwide footprint and expand beyond its traditional retail banking operation.

Stocks of online and discount brokers tumbled on the news. Charles Schwab (down $0.84 to $17.22, Charts) sank nearly 5 percent, while shares of rival Ameritrade (down $2.28 to $16.82, Charts) slid about 12 percent in afternoon trading on Nasdaq.

Given the tough market environment, with retail banks taking a hit from rising interest rates and growing competition for deposits, Bank of America's (Charts) innovation is one way to try to win new deposits and new business as consumers try other products or move assets to the bank.

And if the new pricing model proves successful, that will increase pressure on brokerage firms to lower fees and enhance their offerings in order to compete.

"This is really going to be a battle over the next few years," said Lauren Bender, manager of the wealth management group at independent research and consulting firm Celent LLC. "This is a big threat to brokerage firms because while they may have great technology for financial services, they lack the feet on the ground that some of the banks have."

And that's exactly what Bank of America is counting on. The company, which already has the maximum of 10 percent market share in deposits allowed by regulators and therefore cannot acquire other financial institutions, boasts more than 5,700 retail banking offices across much of the country. Part of the goal of marketing this type of initiative is to convince consumers to do all of their banking in one central place.

Through its brokerage unit, Banc of America Investment Services (BAI), banking customers who have a combined balance of $25,000 in checking, savings and other forms of deposit accounts will be able to qualify for free online equity trades. The company estimates that about 52 million, or 40 percent, of American households will immediately become eligible for this program.

The company will still offer online stock trades for $5 to $10 for all other customers.

Tim Maloney, president of BAI, said in an interview that the company will keep offering its full service investment plan with more than 2,000 financial advisers. But he said the online banking division is growing rapidly, making it a hot market for the company.

"Forty percent of full service customers have online investment relationships someplace," he said. "Our goal is to encourage them to bring more of their business here."

Bank of America said the program is available to customers in the Northeast now and will be rolled out nationwide by February of next year.

And Bank of America's $25,000 minimum is far lower than those offered by competitors. Wells Fargo, (Charts) for instance, offers customers with a $250,000 balance up to 50 free online trades a year. Once consumers surpass 50 trades, they will pay $9.95 for each online trade.

And Charles Schwab customers pay between $9.95 to $12.95 a trade. Those with a million dollars or more in assets pay at the lower end of that range.

Schwab CEO Charles Schwab said his company wasn't overly concerned with Bank of America's offer. "Knowing there is no free lunch, consumers look carefully at the whole picture - rates on their cash, trading costs, quality of services and investment advice, etc.," he said in a statement. "We don't have any plans to change our pricing at this time."

Celent's Bender said the real test will be how well consumers receive Bank of America's new offer. "An active trader that may consider making 30 free trades a month is not only looking at commissions but what kinds of trading tools they offer," she said. "People are increasingly looking for value as opposed to price."

But Brian Moynihan, president of Bank of America Global Wealth & Investment Management, said while the online trading site's analytical tools are high quality, the company isn't looking to attract active traders but rather those with a long-term investment strategy. "30 trades is more trades than our customers are ever going to do," he said.

He added that by providing 30 free trades a month, Bank of America was essentially offering its customers the ability to trade online completely for free. In addition, the bank won't charge online trading customers any annual or management fees.

Still, other brokerages have offered free trading in the past but didn't steal major market share from the big competitors. American Express (Charts), for instance, offered free trades during the height of the dot-com frenzy, but the initiative fizzled because of lack of demand.

Of course, American Express didn't have the same customer base as Bank of America, and that's why this offering may prove to be a real cannonball for other online brokers, Celent's Bender said. "If this works, we'll see a lot more banks going that way," she said. "If brokerages feel they're losing money, you can expect a strong response."

"We think it will be very difficult for any competitors to match this," Moynihan said.

Shares of other some Bank of America competitors came under pressure. Citigroup (Charts) stock sank nearly 1 percent. Shares of Merrill Lyn (down $0.08 to $82.90, Charts)ch moved off early lows to trade little changed.

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