Pilgrim’s Pride continued to process and prepare thousands of chickens in downtown Chattanooga Thursday without 100 workers arrested and dismissed by the company the previous day.

The nation’s biggest chicken supplier lost more than 3 percent of its nationwide production staff when federal immigration agents raided poultry plants in Chattanooga and four other cities Wednesday morning.

“We’ve been working hard today to ensure we continue our operations,” company spokesman Ray Atkinson said Thursday.

But the Texas-based Pilgrim’s Pride, whose officials said they worked with federal authorities to help identify suspected illegal immigrants in its plants, does not face any criminal or civil charges.

While federal prosecutors said Wednesday’s raids show their commitment to enforcing immigration laws, critics said it reflects the difficulties and inequities of current law.

Employers, including those who may unfairly take advantage of immigrant workers, are less likely to be prosecuted, immigration experts said. But Angela Paparelli, a Los Angeles attorney who serves as president of the Alliance of Business Immigration Lawyers, said businesses can’t be expected to verify the accuracy of documents workers provide and shouldn’t target Hispanics for extra review simply because of their race.

“I think this case pointedly illustrates how the current system doesn’t work,” Mrs. Paparelli said. “Employers cannot be document inspectors and, because the identification documents are not easily verifiable, we have a real mess.”

U.S. Attorney John L. Ratcliffe in Tyler, Texas, who is leading the investigation, said in a prepared statement that the probe was focused on individuals who used illegally obtained documents and not on any employers who hired such people.

“We will continue to aggressively prosecute all persons who take someone else’s good name and credit for the purpose of working illegally in this country,” he said.

Pilgrim’s Pride voluntarily participates in E-Verify, the federal program that is supposed to confirm that workers are U.S. citizens. But experts estimated more than 4 percent of the Social Security database has errors.

Linton Joaquin, executive director of the National Immigration Law Center, said current law “puts many low-income workers in a very vulnerable situation.”

“They are subject to criminal prosecution for filling jobs our economy needs,” he said. With millions of undocumented workers in the United States, cases selected for prosecution “are very arbitrary,” Mr. Joaquin said.

Prosecuting a company for employing illegal workers has proven difficult, as evidenced by the biggest such case ever tried. In 2003, a Chattanooga jury ruled that the federal government failed to prove its case against Tyson Foods for hiring illegal workers in Shelbyville, Tenn., and other cities.

Wednesday raid’s came two days after Pilgrim’s Pride announced that, because of the depressed market for chicken, it planned to cut its weekly chicken processing by 5 percent in the second half of the year and close its plant in Siler City, N.C.

Among the 1,800 workers at Pilgrim’s Pride in Chattanooga, federal agents arrested 100 this week on charges of being in the country illegally. Nationwide, 311 Pilgrim’s Pride workers were arrested, including 91 who will face criminal charges in the United States for ID theft or fraud.

Gail Montenegro, a spokesperson for U.S. Immigration and Customs Enforcement, said federal agents are continuing to investigate both workers and managers involved in the case “and further charges could still come.”

Federal authorities involved in this week’s roundup of illegal workers said those arrested were identified during a yearlong investigation and were not selected randomly.