A privately convened commission of labor and immigrant advocates held the first of several planned nationwide hearings yesterday to publicize allegations that U.S. immigration officials routinely violate constitutional protections against unreasonable search and seizure during workplace raids.

At the gathering at the Hay-Adams hotel in the District, witnesses and members of the 10-person panel accused Immigration and Customs Enforcement officials of using arrest warrants for a limited number of illegal immigrants who work at a given company as a pretext to detain the entire workforce, including many U.S. citizens, while agents determine whether there are additional illegal immigrants among them.

"Tens of millions of workers in America go to work every day without . . . an awareness that at their workplaces, without any warning, they could be swept up in a massive raid conducted by heavily armed government agents," said Joe Hansen, president of the United Food and Commercial Workers International Union and chairman of the National Commission on ICE Misconduct and Violations of 4th Amendment Rights. "Workers are not aware that they could be detained at gunpoint. That they could be handcuffed. . . . That they could be denied any contact with family members or legal counsel."

The commission heard testimony from two workers who are U.S. citizens who said they were detained for several hours during an ICE raid of six Swift meatpacking plants in December 2006. The union has filed a class action on their behalf.

Afterward, Pat Reilly, an ICE spokeswoman who attended the hearing as an observer, said the agency's procedures for questioning workers during raids at businesses are fair and humane and have been routinely upheld by courts.

"I would imagine that some people may be detained beyond what they feel is reasonable. But it's subjective," she said. "What we're trying to do is get to the bottom of who has the right to be here and who might be posing as a U.S. citizen."