A lawsuit was filed in federal court Tuesday accusing I.B.M. of denying overtime pay to tens of thousands of workers.

The suit, which seeks class-action status nationwide, contends that the company violated federal and state labor laws in California and New York by misclassifying full-time computer installation and maintenance workers as exempt from overtime.

"We believe that those tens of thousands of workers have worked tens of thousands, perhaps millions, of unpaid overtime hours," James M. Finberg, a lawyer at Lieff Cabraser Heimann & Bernstein, said at a news conference in San Francisco, where the suit was filed.

Employees working more than 40 hours a week are generally entitled to overtime pay under federal law, unless they fall under specific legal exemptions. The plaintiffs in this suit do not "fall into the very narrow exceptions to the overtime laws," Mr. Finberg said.

The suit names as plaintiffs two current I.B.M. employees in California, Thomas Rosenburg and John Shelly, and one former employee in New York, Exaldo Topacio, who worked for I.B.M. for a year beginning in March 2003. I.B.M. is based in Armonk, N.Y.

"There were many occasions when I was required to work in excess of 40 hours per week," said Mr. Topacio, a former technical support worker in I.B.M.'s New York network support division, responsible for installing and maintaining computer software and hardware.

Mr. Topacio, who worked for another computer company before I.B.M., also said that such violations were commonplace in the industry, where workers typically earn $40,000 to $60,000 annually.

Mr. Topacio said that I.B.M. informed him and his colleagues that under the law, they were exempt from overtime pay.

In a phone interview, John Bukovinsky, an I.B.M. spokesman, said: "The company does not comment on pending or on ongoing litigation. We're reviewing the documents."

The suit seeks compensation for unpaid overtime nationally and, in California, it also seeks an injunction against I.B.M. to stop what the plaintiffs call unfair labor practices regarding unpaid overtime.

The plaintiffs are also likely to seek additional damages equal to double the compensatory overtime, arguing that I.B.M. should have investigated and followed federal overtime laws but did not, Mr. Finberg said.