WASHINGTON — Federal labor mediators have advised the Education Department that it most likely imposed new work rules on its employees illegally, curtailing workers’ protections and access to union representation in violation of federal law.

The American Federation of Government Employees said Tuesday that the Federal Labor Relations Authority advised the Education Department that it had engaged in “bad-faith bargaining” when it implemented a contract this year that gutted compensation and benefits provisions for the department’s 3,900 employees, and limited employees’ ability to carry out union duties during the work day.

The decision could have broad implications because the Education Department’s actions mirror Trump administration efforts throughout the federal government. The Social Security Administration and the Department of Veterans Affairs have begun implementing work rules similar to the ones at the Education Department, union officials said. And many of the anti-union elements reflect a series of executive orders on the federal work force that President Trump signed in May.

The union plans to use the finding as it pursues labor disputes across the federal government.

“For the first salvo to be knocked down by the F.L.R.A., it sends the message that the government isn’t going to be allowed to operate outside the bounds of the law,” said David A. Borer, general counsel for the union.