On July 1, Homeland Security Secretary Janet Napolitano announced an audit of employers to verify whether their employees were eligible to work. Mr. Morton said that 654 companies are currently being audited and that many more employers will be notified soon that they also will be under scrutiny by the government.

Tom Roach, an immigration attorney in Pasco, Wash., said that apple, cherry and grape growers in his area are panicking over the new crackdown. Few industries have come so close to admitting they cannot survive without the labor of illegal immigrants as agriculture. At least half of the 1.8 million crop workers in the U.S. are undocumented.

Mr. Roach said a client who received a notification of inspection from ICE last month could face thousands of dollars in fines. "There is a ton of counterfeit documents out there. The employer does exactly what he is supposed to do, but he can still get in trouble," he said.

As part of the audit, immigration agents review the I-9 forms and other records of a company. If agents conclude that a business knowingly hired illegal workers, criminal investigations follow.

On Monday, federal prosecutors filed charges against Bellingham, Wash.-based Yamato Engines Specialists where 28 people were arrested in a February immigration raid, accusing the family-owned business of knowingly hiring illegal immigrants. The raid at Yamato was the first since President Barack Obama took office and attracted national attention. Calls to Yamato Engine weren't immediately returned Monday, the Associated Press reported.

Fines for companies found to employ workers in the country illegally could exceed $800 per employee. "You have to make sure that the fine isn't just seen by these companies as part of their bottom line," said deputy ICE chief Alonzo Peña. Messrs. Morton and Peña said the government would promote use by companies of an electronic employment verification system, known as E-Verify. The system is voluntary in California and most states.

Enforcement activity during the Bush administration focused on high-profile raids in which thousands of illegal immigrants were arrested and placed in deportation proceedings. Relatively few companies and their executives were prosecuted.

The Obama administration has made employers the cornerstone of its immigration policy. "If we are going to have serious change, we must make sure the employer community is complying with the law," said Mr. Morton, referring to employers as the magnet that attracts thousands of illegal workers to the U.S. each year.

About 11.5 million illegal immigrants live in the U.S., according to the Pew Hispanic Center, a nonpartisan research group. Without illegal immigrants, business executives in industries like construction, lodging and agriculture say they would be forced to radically change how they operate. http://www.greencardapply.com/news/news09/news09_0823.htm