By ERIC LIPTON

WASHINGTON, April 20— The apprehension on Wednesday of more than 1,100 illegal immigrants employed by a Houston-based pallet supply company, as well as the arrest of seven of its managers, represents the kickoff of a more aggressive federal immigration enforcement campaign intended to hold employers accountable for breaking the law, Homeland Security Secretary Michael Chertoff said today.Saying the hiring by companies nationwide of millions of undocumented workers is often a form of organized crime, Mr. Chertoff, a former federal prosecutor, said the government will now attempt to combat the practice with techniques similar to those used to try to shut down the mob.