Five U.S. senators have questioned a ploy used in July by federal immigration officials to arrest dozens of immigrants working without proper documents at Seymour Johnson Air Force Base in North Carolina, the Associated Press reports.

The immigrants on construction crews were told to attend a safety meeting, but 48 were arrested once they arrived.

The senators said in a letter to Homeland Security Secretary Michael Chertoff that they support efforts to enforce the law, but are concerned the tactic will undermine workplace safety training.

Democratic Senators Russell Feingold of Wisconsin, Ted Kennedy of Massachusetts, Patty Murray of Washington and Patrick Leahy of Vermont, along with Vermont Independent Jim Jeffords signed the letter.

A spokeswoman for the federal Immigration and Customs agency says the tactic was accepted in law enforcement and assured a safe arrest.