San Francisco ? The Social Security Administration cannot start sending out letters to employers next week containing notification of more serious penalties for knowingly hiring illegal immigrants, a federal judge ruled Friday.

Ruling on a lawsuit by the nation’s largest federation of labor unions against the U.S. government, U.S. District Judge Maxine Chesney granted a temporary restraining order prohibiting the so-called “no-match” letters from going out as planned starting Tuesday.

The AFL-CIO lawsuit, filed this week, claims that new Department of Homeland Security rules outlined in accompanying letters threaten to violate workers’ rights and unfairly burden employers. Chesney said the court needs “breathing room” before making any decision on the legality of new penalties aimed at cracking down on the hiring of illegal immigrants.