The National Treasury Employees Union has filed a lawsuit to block an executive order signed by President Trump last week that threatens to remove civil service protections from much of the federal workforce, allowing employees to be fired at will by supervisors and new employees brought in who support the politics of whichever administration is in power.

With little fanfare, Trump signed Executive Order 13597, which would create a new Schedule F that would reclassify federal employees and make it easier to hire or fire them, regardless of experience or behavior.

“Separating employees who cannot or will not meet required performance standards is important, and it is particularly important with regard to employees in confidential, policy- determining, policy-making, or policy-advocating positions,” said the order. “High performance by such employees can meaningfully enhance agency operations, while poor performance can significantly hinder them. Senior agency officials report that poor performance by career employees in policy-relevant positions has resulted in long delays and substandard-quality work for important agency projects, such as drafting and issuing regulations.”

The executive order is facing challenges from Democrats, who have introduced legislation to stop it, as well as the NTEU, which represents employees of the Internal Revenue Service, the Treasury Department and about 30 other federal agencies and departments. They fear that the order will be used to root out experienced federal workers who have traditionally enjoyed civil service protections by accusing them of being disloyal to the current administration. It could allow a revival of the so-called “spoils system” of political patronage that the merit-based civil service system aimed to eliminate back in the 19th century. The NTEU filed a lawsuit Monday in the U.S. District Court for the District of Columbia, naming as defendants Trump and Michael Rigas, acting director of the Office of Personnel Management.

The NTEU noted that Trump has also ordered agency leaders to identify which employees should be forced to lose the civil service protections they are entitled to under the law, enabling them to be hired or fired at will for purely partisan reasons.

“The president is attempting to run roughshod over the separation of powers and rewrite the law himself in a way that threatens a critical pillar of our democracy, and someone has to stand up to him,” said NTEU national president Tony Reardon in a statement Tuesday. “NTEU is proud to do so, with this lawsuit as well as supporting those in Congress who are pursuing legislative efforts to block the order.”

A group of House Democrats introduced a bill, known as the Saving the Civil Service Act, which would rescind Trump’s executive order removing civil service protections from an entire class of employees and prevent the use of government funding to implement it. The bill was introduced by House Majority Leader Steny Hoyer, D-Maryland, House Committee on Oversight and Reform chairwoman Carolyn Maloney, D-New York, and House Oversight and Reform Subcommittee on Government Operations chairman Rep. Gerry Connolly, D-Virginia.

“We commend Congress for quickly recognizing this executive order for the threat that it presents to the professional, merit-based civil service,” Reardon said in a statement. “We strongly support the Saving the Civil Service Act because it will safeguard the principle that federal employees swear an oath to the Constitution and work for the taxpayers, not the president.”