(FORTUNE Magazine) – Companies are getting even tougher on cigarette fiends now that the Environmental Protection Agency has declared that secondhand smoke causes cancer. Employers such as PepsiCo, Federal Express, Du Pont, US West, and Ralston Purina -- in total, one-third of the corporations that make up FORTUNE's Industrial 100 and half the 50 largest diversified service companies -- say no to smoking inside all their facilities. John Pinney, CEO of Corporate Health Policies Group, a consultant in Bethesda, Maryland, surveys these companies annually and says, ''I expect a big increase in smoking bans this year.'' At the most health-conscious outfits, employees cannot puff anywhere, even outdoors. Merck, the New Jersey-based drugmaker, imposed such a ban in 1989, after a one-year warning. Smoking is a nasty habit to break, of course. Managers at Glaxo Holdings, the British pharmaceutical company, watched body counts in the company's U.S. cafeterias drop once smoking was outlawed. The hopelessly hooked go off premises to light up. Comsat, the telecommunications company in Washington, D.C., cut smoking demand by effectively raising the price. Management banned smoking on Comsat properties worldwide in 1991 and then jacked up out-of-pocket health care costs for smokers, who now pay twice as much as nonsmokers for health insurance. About 10% of the work force is still puffing, vs. some 25% before the rules changed. Says James Helms, employee relations manager at Comsat: ''We're making cigarette smoking as inconvenient as we possibly can -- and so we should as secondhand smoke becomes an increasingly important issue.'' These words, mind you, come from a pack-a-day puffer. And that's after cutting his consumption in half. Helms now calls himself a ''vampire smoker.'' He explains, ''I smoke only at night.''