POSTVILLE - Members of Iowa's congressional delegation are questioning whether federal immigration officials should start looking at penalizing Agriprocessors after more than a third of its work force was arrested during a raid Monday.

U.S. Congressman Bruce Braley of Waterloo wrote a letter to the U.S. Immigration and Customs Enforcement, which conducted Monday's raids, urging them to "fully investigate" Agriprocessors for possible immigration law violations. The raid - called the largest of its kind in the nation - netted 390 arrests, or about 40 percent of the work force.

"This figure alone raises questions about Agriprocessors' commitment to making sure they have a legal work force," Braley wrote.

At least 20 people face criminal charges related to fraud and identity theft, but no company officials have been charged.

Braley said there needs to be a greater emphasis on punishing employers who knowingly hire illegal immigrants as a way to curb the immigration problem.

In 2004, just three employers were fined for breaking those laws. Four years later - after the Bush administration announced employer enforcement would be a priority - 92 employers were arrested and 17 fined, Braley said.

U.S. Sen. Tom Harkin said the Postville case created "troubling questions" about Agriprocessors' hiring process. He also asked for a full investigation into the claims and that any violations of immigration law be prosecuted.

"I have always supported vigorous enforcement of our immigration laws, but we have to enforce our laws equally," he said. "If employers are knowingly hiring undocumented workers, they must be held accountable."

Members of Braley's staff toured the National Cattle Congress grounds Wednesday, where the 390 detainees are being held.

"There's a lot of information going around, and with information comes rumor and all of that stuff," said Jeff Giertz, a Braley spokesman who visited the grounds. "It's tough figuring out what's out there, what's not out there."

Representatives for Sens. Charles Grassley and Harkin were also in attendance. The representatives were interested in seeing the conditions at the facility.

"This is a very serious situation and it's important that federal officials be as transparent as possible," Grassley said in a statement.

Giertz said the group was not able to speak to any of the detainees, but he said they were able to see how the intake process functioned.

"I think there's no question that the federal agencies there are running a professional operation," he said.

Grassley said he was happy to see ICE officials learned a few lessons after taking criticism for their actions during a December 2006 raid on Swift packing plants in six states, including the plant in Marshalltown.

Those changes included access to court-appointed attorneys and bilingual handbooks explaining the process. Most importantly, he said, was the fact that ICE was releasing parents if no one was available to care for children.

The NCC fairgrounds are being used until federal officials determine whether to file criminal charges. Those who are charged will be turned over to U.S. marshals. Those who aren't charged will remain in ICE custody and transported to an area immigration detention facility for removal proceedings.

Giertz said ICE officials declined to comment on whether Agriprocessors would be facing any charges.

Agriprocessors put out a statement Tuesday stating it was cooperating with ICE officials and other government agencies.

"Our company takes the immigration laws seriously," the statement said. "We cooperated with the government in the enforcement action. We intend to continue to cooperate with the government in its investigation."

Company officials also said they plan on investigating the incident.

They also extended their sympathies to families who were affected by the raid.

Contact Josh Nelson at (319) 291-1565 or josh.nelson@wcfcourier.com.