Amid heightened tensions between the United States and Iraq and continued concerns about terrorism, the U.S. Equal Employment Opportunity Commission has renewed its message to employers that it is illegal to discriminate against foreign-born workers.

The agency issued updated anti-bias guidelines yesterday that underscore its post-Sept. 11 message to employers -- particularly small businesses -- that they are responsible for unfair actions taken against workers on the basis of national origin. The guidelines had last been issued in 1980, and there has since been a marked increase in immigrants in the workforce.

The agency has posted on its Web site hypothetical examples of what would be considered illegal activities. It cited, among others, a Christian Egyptian who is harassed by co-workers about his Arab ethnicity but whose employers do not intercede on his behalf, a Lebanese cabdriver dismissed because customers said they were afraid to ride with him and harsher disciplinary treatment given to Muslims than workers of other faiths.

"Immigrants have long been an asset to the American workforce," EEOC Chair Cari M. Dominguez said in a statement. "Recent world events, including the events of September 11, 2001, only add to the need for employers to be vigilant in ensuring a workplace free from discrimination."

In the weeks after last year's terrorist attacks, the commission was criticized by some Arab-American groups for what they said was an ineffectual response to widespread reports of workplace discrimination against Arab Americans. Agency officials said they would enforce anti-bias laws and vigorously pursue any allegations that could be substantiated.

The commission has since filed national-origin lawsuits against several employers, including an aerospace manufacturer in Tampa and an art museum in Worcester, Mass., that were alleged to have fired Arab-American workers soon after the attacks.

Three weeks ago the agency reached a $35,000 settlement with a kidney-dialysis center in North Carolina where an employee said she had been subjected to a hostile work environment after last year's terrorist attacks. The worker, a licensed practical nurse, told the agency she converted to Islam shortly before the attacks and began wearing a religious scarf to work within a month after Sept. 11, 2001. She said her employer said her appearance was frightening the center's mostly elderly patients, and she quit. The commission said she had in effect been forced to quit.

Terence D. Friedman, an attorney for the medical clinic, said his client disputed the woman's version of events but settled to avoid prolonged litigation. "We felt it was an instance of overreaching by the government," he said.

Eric Siegel, an attorney for workers, said one client, named Osama, had said that co-workers began interrogating him about his religious beliefs after Sept. 11 and told Osama that they didn't want to work with him anymore. Then a manager at the D.C. store where he worked called Osama into his office, questioned him about a theft that had occurred and fired him on the spot. Siegel said his client is considering a lawsuit.

The EEOC received 8,025 reports of national-origin discrimination in the year ended Sept. 30, up slightly from 7,792 the previous year. About 10 percent of all discrimination claims brought to the agency involve national-origin discrimination, a proportion that has remained relatively steady for the past decade. Race, sex and age discrimination remain the three biggest sources of bias complaints brought to the agency.