Washington ? The government plans to crack down ever harder on employers who harbor and hire illegal immigrants, pursuing companies that ignore the law so they can exploit cheap labor.

“We are going to move beyond the current level of activity to a higher level in each month and year to come,” Homeland Security Secretary Michael Chertoff said Thursday. He pledged to “come down as hard as possible” on violators.

Federal agents on Wednesday arrested seven current and former managers of IFCO Systems, a manufacturer of crates and pallets, on criminal charges, and more than 1,100 people were arrested on administrative immigration charges at more than 40 IFCO sites in the U.S.

More than half of the company’s roughly 5,800 employees during 2005 had invalid or mismatched Social Security numbers, the government alleges.

The case began after officials received a tip that IFCO workers in Guilderland, N.Y., were seen ripping up their W-2 forms because they did not intend to file tax returns, Chertoff said.

Six of seven current and former IFCO managers charged with felony conspiracy to harbor illegal aliens were released on bond. The managers could face up to 10 years in prison and a $250,000 fine for each alien involved, as well as forfeitures.