San Francisco-based employment lawyer Stephen Hirschfeld went on a business trip to Shanghai and Tokyo six weeks ago, and he came home sick. He has had difficulty breathing and his chest feels congested, and although his doctor has assured him he has not contracted severe acute respiratory syndrome, he's been frightened.

His clients are frightened, too, he said, as they worry over the potential business impact of the new disease. Those concerns were heightened yesterday when the Centers for Disease Control and Prevention issued an advisory that told workers and their employers to be "vigilant" for signs of fever and respiratory ailments among their employees who have traveled recently to mainland China, Hong Kong, Singapore and Hanoi. The agency urged people with those symptoms to quarantine themselves at home and seek medical care.

"I represent a lot of companies that do business in the Pacific Rim," Hirschfeld said. "It's a logistical problem that's a nightmare. What are companies supposed to do with employees that are supposed to go over there, what if they are too afraid to go, and also what to do about their expatriates, and should we be bringing them home?"

Robert Sherretta, vice president of the International Trade Association of Northern Virginia and owner of a foreign-investment firm, said he attended a conference at the World Bank yesterday that brought together businesspeople from around the world. Some attendees expressed concern that they could get sick just by shaking hands with ill people, he said.

"It may be more psychological than real . . . but it occurs to everybody now that people are coming off airplanes where they might have been exposed to disease," he said.

In the past six months, 3,169 people have fallen ill from SARS, and 213 have died, according to the World Health Organization, with the vast majority of cases on mainland China, the epicenter of the outbreak. The international health group reported that 174 people in the United States and 100 in Canada have contracted the illness. Many victims fell ill after traveling in Asia or having close contact with people who had.

The issue is complicating the ever-growing trade links between the United States and Asia, as companies deliberate over whether the production lines overseas can be supervised electronically, by e-mail or teleconference.

At the International Labor Organization, a United Nations agency, the issue isn't just theoretical. One week ago, a Finnish labor expert, Pekka Aro, 52, became ill and died from SARS while in China preparing for an employment forum. His ILO colleagues in Beijing, and their families, were placed in quarantine.

The group banned travel by its staff to China on April 2. On April 10, the organization announced that its planned meetings in Toronto, Hong Kong, Taiwan, Singapore and Vietnam have been postponed "until further notice."

J. Craig Shearman, a spokesman for the National Retail Federation, whose member companies import an increasing percentage of the goods they sell from Asia, said "a number of retail companies" similarly have restricted their employees' travel to Asia "until this issue can be resolved."

Many companies are relying on their branch offices in those countries to oversee production until the illness fades or scientists find better ways to treat it, he said. "It may not be necessary to go there at all," Shearman said, adding that "site visits to inspect are more about building relationships."

"Actual people don't need to travel back and forth," he said.

But Matthew Shapiro, director of marketing for Social Accountability International, which monitors workplace conditions abroad, including at 39 sites in China, said the disease has struck hardest in the region he called "the cradle of light manufacturing in China."

"It's very important culturally and technologically to be able to send your staff to where your goods are made," Shapiro said, adding that a lack of corporate oversight could lead to worsening working conditions in Asian factories.

Francis P. Alvarez, an employment lawyer in White Plains, N.Y., said he and colleagues also are fielding calls from worried employers. Some wonder whether they should tell workers who have been in Asia recently to go home, even if they are not ill, because they may be symptom-free carriers of the ailment. He said some workers don't want to go home because they fear missing work.

"No matter what an employer does, he faces risk," Alvarez said. "It's a difficult situation for them. But like all other types of crises, like the anthrax scare, employers are well served to try to educate their employees with information on the health risks so as not to perpetuate inaccurate information. . . . This is something employers need to be watching day to day."