The Department of Homeland Security said Friday that it is ending the collective bargaining agreement with the tens of thousands of frontline employees at the Transportation Security Administration, marking a major effort to dismantle union protections under the Trump administration.

The TSA union called it on “unprovoked attack” and vowed to fight it.

The department criticized the union whose staffers are responsible for keeping weapons off airplanes and protecting air travel. Officials said that poor performers were being allowed to stay on the job and that the agreement was hindering the ability of the organization “to safeguard our transportation systems and keep Americans safe” — an assessment that faced immediate pushback from a top Democrat in Congress and the union.

“This action will ensure Americans will have a more effective and modernized workforces across the nation’s transportation networks,” the agency said in a statement.