The Federal Bureau of Prisons said on Thursday that it was canceling a collective bargaining agreement with the union representing more than 30,000 prison workers, making it the latest group to be targeted by the Trump administration’s effort to assert more control over the government work force.

William K. Marshall III, the bureau’s director, told employees that he was terminating the contact with the union, the Council of Prison Locals, saying that it had become an obstacle to making changes intended to improve safety and morale.

He said that workers would not be removed, suspended or demoted without cause or due process, and that their pay and benefits were guaranteed by law and would remain.

Brandy Moore White, the union’s president, said that terminating the contract would deprive employees of essential labor rights, including ways to address workplace problems like forced overtime and safety concerns.

“Don’t be fooled, this is not about efficiency or accountability — this is about silencing our voice,” she said in a statement, adding that the union was prepared to take legal and legislative action to protect the contract.

The Bureau of Prisons oversees 155,000 inmates in 122 facilities across the United States and has more than 34,800 employees, according to its website.

President Trump’s executive orders since March have stripped nearly half a million federal workers of union rights. He issued an executive order in March instructing a broad swath of government agencies to end collective bargaining with federal unions. That order targets agreements covering nearly a million federal workers at agencies including the Justice Department, of which the prisons bureau is a part.

The president has cast his instructions as necessary for national security. The unions targeted in the orders have repeatedly sued the administration, calling them acts of retaliation against unions. A federal appeals court has ruled in favor of Mr. Trump.