(Reuters) - President Donald Trump signed an order within hours of taking office on Monday to make it easier to fire thousands of federal agency employees and replace them with political loyalists. The order, which is largely identical to one Trump issued late in his first term, is already facing a lawsuit by a major union and is likely to trigger more legal challenges.

WHAT DOES THE ORDER DO?

The vast majority of the more than 2.2 million employees of the federal government are career civil servants who are hired on merit and serve the government as a whole. Civil service positions do not terminate at the end of an administration and civil servants can only be fired for cause.

During past presidential administrations a few thousand federal jobs have been considered political appointments. Trump's order creates a new much larger category of federal employees called "Schedule Policy/Career" who do not have the typical protections enjoyed by civil servants and can be fired at will. It applies to jobs "of a confidential, policy-determining, policy-making, or policy-advocating character."

Trump has for years criticized the federal bureaucracy, which he calls the "deep state," claiming civil servants are unaccountable because they are insulated from losing their jobs. The new order will give Trump the power to fire as many as 50,000 of those workers and replace them with political loyalists.

HOW CAN THE PRESIDENT EXEMPT WORKERS FROM THE CIVIL SERVICE?

Congress gave the president the power to exempt positions from the civil service when "necessary" and "as conditions of good administration warrant." Trump in his order said creating Schedule Policy/Career was necessary to give agencies more flexibility and discretion in hiring. He said the order was a response to "numerous and well-documented cases of career federal employees resisting and undermining the policies and directives of their executive leadership."

WHAT HAPPENED TO TRUMP'S FIRST ATTEMPT TO RECLASSIFY FEDERAL WORKERS?

Trump first carved out the exemption in a 2020 executive order during his first administration, at the time calling it Schedule F. But Democratic former President Joe Biden rescinded the order in 2021, before any workers were reclassified. Trump's order had faced an immediate legal challenge from the National Treasury Employees Union, which represents 150,000 employees at 37 federal agencies. The case was rendered moot when Biden withdrew the order.

The NTEU sued again late Monday, claiming that the new order improperly strips federal workers of their due process rights and that Trump had failed to explain why the new order was necessary, as required by federal law.

CAN THE ORDER TAKE EFFECT IMMEDIATELY?

No. The Biden administration passed a rule in 2024 intended as a bulwark against Trump's resurrection of Schedule F. The rule says workers who are involuntarily exempted from the civil service retain the legal protections they had already earned, and created a process for them to challenge their reclassification. The U.S. Office of Personnel Management is expected to propose repealing the rule, a process that would take months or longer.

The order gives agency heads 90 days to conduct a preliminary review and 210 days to complete a full review of positions that could be transferred to the new category.

CAN WORKERS SUE OVER BEING EXEMPTED?

Unions are certain to file legal challenges, but individual workers who are reclassified under the new order would have to go through an administrative process before the Merit Systems Protection Board, an independent three-member panel appointed by the president. Until the 2024 rule is repealed, workers who are reclassified could take advantage of the process it created to appeal those decisions to the merit board.

Employees could argue their jobs fall outside the scope of Schedule Policy/Career, that agencies violated their due process rights by not following the proper procedures, or that they were targeted for discriminatory reasons.