The judge determined that Trump’s effort to throw out collective bargaining rights for TSA screeners was probably illegal.

The Trump administration faced another legal setback on Monday when a judge temporarily blocked their plan to dissolve labor unions at a federal agency.

The White House moved in March to revoke collective bargaining rights at the Transportation Security Administration, aiming to nullify the union contract for some 47,000 airport security officers. But U.S. District Judge Marsha J. Pechman in Seattle, Washington, granted an injunction Monday at the request of the union, the American Federation of Government Employees.

Pechman, an appointee of President Bill Clinton, determined that the union was likely to prevail in its argument that the administration ran afoul of the law. She said Trump’s homeland security secretary, Kristi Noem, offered only a “threadbare justification” for stripping workers of their union rights, and the move appeared purely retaliatory.