(Reuters) - Five unions sued the Trump administration on Wednesday, seeking to block what they called the possible mass firing of hundreds of thousands of federal employees who resist pressure to accept buyouts.

In a complaint filed in Washington, D.C. federal court, the unions accused the White House and others in the Executive Branch of undermining Congress' role in creating and funding a federal workforce, violating separation of powers principles.

The plaintiffs include the United Auto Workers, the National Treasury Employees Union, the National Federation of Federal Employees, the International Association of Machinists and Aerospace Workers, and the International Federation of Professional and Technical Engineers.

Ten defendants were named, including Trump, the heads of agencies, the Department of Defense, Internal Revenue Service and Consumer Financial Protection Bureau, and the acting director of the Office of Personnel Management.

Last week, some unions sued the Trump administration to block the buyouts. On Monday, U.S. District Judge George O'Toole in Boston kept in place a block of the buyout plan for federal employees, as he considers whether to impose it for a longer period of time.

The decision prevents Trump's administration from implementing the buyout plan for now, giving a temporary victory to labor unions that have sued to stop it entirely.

On Tuesday, meanwhile, Trump ordered U.S. agencies to work closely with billionaire Elon Musk's Department of Government Efficiency to identify federal employees who could be laid off.