In an effort to crack down on illegal labor, the Department of Homeland Security intends to step up enforcement efforts against employers who knowingly hire such workers.

Under guidelines to be issued to Immigration and Customs Enforcement field offices, agents will be instructed to take aim at employers and supervisors for prosecution “through the use of carefully planned criminal investigations.”

Senior officials of the Homeland Security Department said Wednesday that illegal workers would continue to be detained in raids on workplaces. But the officials said they hoped to mark an abrupt departure from past practices by making those arrests as part of an effort to build criminal and civil cases against employers.

Under the Bush administration, the officials said, most raids were conducted largely on the basis of tips that an employer was hiring illegal workers, rather than on information gleaned from audits of employer records or undercover investigations. As a result, agents rounded up thousands of illegal immigrants but rarely developed the evidence necessary to show whether businesses were knowingly using illegal labor…

“Enforcement efforts focused on employers better target the root causes of illegal immigration,” say the guidelines, a copy of which was obtained by The New York Times. “ICE must prioritize the criminal prosecution of actual employers who knowingly hire illegal workers because such employers are not sufficiently punished or deterred by the arrest of their illegal work force.”

Overdue.