For most of the 11 years that Irma Rivera sold crystal for Baccarat Inc., one of Manhattan's most exclusive purveyors of fine glass, her ability to speak both Spanish and English was a clear benefit. A supervisor once praised her work, saying she was a sales leader in part because her bilingualism made her "extremely effective when dealing with South American and other Spanish-speaking customers."

But what was once one of Rivera's most valued assets eventually led to her professional undoing. She was fired in 1995, in part, she said, because she spoke Spanish to a co-worker on the job in violation of store policy.

Earlier this year, a federal jury awarded Rivera $500,000, marking what employment lawyers say is the first time that damages were awarded in a case challenging an employer's English-only policy.

Few activists who monitor this burgeoning civil rights issue think it will be the last.

As the ranks of the nation's immigrants swell, so have the number of employers requiring workers to speak English at all times on the job, a prohibition that many civil rights activists call discriminatory. Over the past three years, the federal Equal Employment Opportunity Commission has received 363 complaints from people claiming that such policies are discriminatory, a figure that has doubled in the past two years alone. Civil rights attorneys also report a sharp increase in discrimination lawsuits challenging what they describe as a proliferation of English-only policies.

"I think this is part of a kind of backlash about immigrants," said Ed Chen, a lawyer with the American Civil Liberties Union of Northern California. "There is a general level of discomfort when there are a lot of immigrants around. Language becomes something of a flash point for some of those insecurities."

Under federal law, employers are within their rights to demand that workers speak English, but only if that restriction is necessary for conducting business. EEOC rules say that employers cannot prohibit employees from speaking a foreign language in informal situations. But the legal soundness of those guidelines was challenged by a 1993 federal appeals court ruling upholding an English-only restriction at a California meat processing company. There, employees who spoke only English had complained that they were being harassed in Spanish by co-workers.

Federal officials say the laws governing English-only restrictions often are misunderstood or ignored by employers who become unnerved by employees speaking a language they don't understand. For years, for example, convalescent homes in California commonly prohibited employees from speaking foreign languages if they were within "earshot" of patients. Chen said that restriction was even enforced by state health inspectors, who erroneously thought those policies were required by federal patients' rights law.

That prohibition was overturned two years ago when a Gilroy, Calif., convalescent home settled a suit brought by a former employee who was fired for speaking Spanish to a co-worker. After the settlement, California health officials issued new guidelines making it clear that employees are not required to speak English unless they are talking to patients or actively engaged in performing some type of service for them.

Employers accused of illegally imposing English-only rules typically see them as common-sense restrictions aimed at keeping the workplace comfortable for those who speak only English.

"Some managers feel they need English-only rules to maintain control in the workplace," said Caroline Zambrowicz, a spokeswoman for the Society for Human Resource Management. "Sometimes people feel others are talking behind their back if they use a foreign language. It can create an uncomfortable atmosphere."

Such sentiment is not new. In the 1920s, fear of the nation's large influx of immigrants led several states to ban the teaching of foreign languages in public schools. But with immigrants now accounting for 11 percent of the nation's labor force, language rights activists see imposition of English-only policies in the workplace as part of a larger anti-immigrant backlash. Many call the workplace restrictions a direct outgrowth of the movement that has resulted in English being declared the official language in 25 states, a designation that is often symbolic but in some cases has restricted non-English services provided by state governments.

"This English-only rhetoric has seeped into the fabric of the nation," said Juan A. Figueroa, president of the Puerto Rican Legal Defense and Education Fund, a Manhattan-based advocacy group that has brought several lawsuits in recent years challenging English-only policies. "It is especially troubling because language is so closely tied to one's national origin."

Many employers contend that they craft English-only policies to complement their business needs or protect the rights of English-speaking workers. But language rights activists complain that language restrictions are often imposed at the whim of supervisors who find themselves uncomfortable among workers who speak languages other than English.

Maria Quinones and Evelyn Silverman were fired from their jobs as home health care workers in May 1995, shortly after their supervisor at a Brooklyn-based home nursing firm warned them not to speak Spanish on the job.

The women, who are from the Dominican Republic, alleged that they were fired after the same supervisor heard them speaking Spanish on the sidewalk outside the firm's offices. The EEOC has filed a lawsuit against the company, which has denied the charge, saying the women were fired "for cause." The suit is pending in federal court.

Similarly, the EEOC settled a suit earlier this month, winning a $133,000 payment for six employees from NHS National Health Services Inc. and EMS Correctional Care Inc., New York firms that provided health services at juvenile correction facilities. Among the charges made by the EEOC was that a supervisor with a mostly Latino work force imposed an "English-only" rule that extended to employees' personal activities at work.

"They were not allowed to speak Spanish during breaks, or at lunch, and they were not allowed to listen to Spanish radio stations," said Elizabeth Grossman, an EEOC trial attorney who handled the case.

In the Baccarat case, store lawyers said Rivera was fired by a new company president as part of a shake-up intented to improve the store's sales performance. The new president had made several unannounced visits to the Madison Avenue store and found that the sales force was not friendly or attentive enough, company lawyers said.

In court, the company president acknowledged that Rivera was ordered to refrain from speaking Spanish. But he said the rule was imposed as "a matter of courtesy" to employees and customers who speak only English. The jury wasn't convinced, and Baccarat's request for a new trial was denied.

The requirement to speak English has at times affected even employees who have little contact with either the public or other workers.

Rogelio Campos, 61, a dump truck driver who moved to the United States from Cuba 14 years ago, was stopped by police in Yonkers, N.Y., last summer, allegedly because his dump truck was overweight. But after talking with the officer, Campos was given a ticket under an obscure section of federal transportation law that prohibits drivers from operating commercial vehicles if they don't have an adequate command of English. Campos is fighting the case in court with the help of the Puerto Rican Legal Defense and Education Fund.

"This is a guy who has never run a stop sign," said Fernando Mateo, a Dominican immigrant who owns San Mateo Construction Corp., which employs Campos. "The funny thing here is that he was able to take a test for his commercial license in Spanish, but he is required to speak English."

Mateo, 40, who owns several companies after starting out as a poor high school dropout, said learning English has been integral to his success. He has used the incident to prod Campos into taking classes to improve his limited English. Still, he thinks the police went too far by giving his driver a ticket.

"You are a nobody in this country if you can't speak English. I am a firm believer that if I live in France, my language should be French. If I live in Spain, my language should be Spanish. If I live in the United States, my language should be English," Mateo said. "But I don't feel that, constitutionally, anyone should be given a ticket because they can't speak the language."