Donald Trump’s return to office sets the stage for harassment, intimidation and “old-fashioned corruption” to spread throughout the US federal government, a top union leader has warned.

The president-elect and his allies have expressed support for the mass firing of civil service workers and abolishing certain government agencies upon his return to the White House.

Officials at the heart of Trump’s first administration have spoken of purging thousands of federal workers by using controversial powers to reshape the bureaucracy. Now, inside dozens of government agencies, staff are bracing for Trump’s second administration.

“It’s pretty bleak,” said Steve Lenkart, executive director of the National Federation of Federal Employees, which represents 110,000 employees at various agencies around the US. “It’s pretty grim.”

The former president attacked federal employees on the campaign trail, claiming they were “destroying this country” in an August podcast interview. “They’re crooked people, they’re dishonest people,” he said. “They’re going to be held accountable.”

Trump has signaled his support for reviving the Schedule F executive order he issued in the final days of his last administration, under which swaths of the federal workforce could be stripped of their civil servant protections and redefined as political appointees. Advocates of the policy claimed to have identified 50,000 employees that could be fired.

“It’s probably been 150 years since we had something like this happen,” Lenkart said, pointing to the Pendleton Act, which in 1883 mandated that federal employees be hired based on merit, subject to competitive exams, and protected from political influences.

“One hundred and fifty years of hard lessons learned are all erased,” he said. “And now you’ve taken away that ability for federal employees to report bad things they see; you take away the ability of an employee to resist an illegal order, or an order that’s a political overreach of some kind, or simply a threat of old-fashioned corruption, stealing stuff, helping someone gain a market or consolidate their personal wealth.

“It’s old-fashioned corruption that is going to come back, too, because of people looking to make money off of this authority that federal employees have.”

Schedule F allows an unlimited number of political appointees to be hired into the federal government, as direct hires with no expiration date based on presidential terms, Lenkart said.

The success of Project 2025, the rightwing plan for Trump’s presidency, “revolves around” the implementation of Schedule F, he added: reclassifying roles typically filled by career government employees as political, “and having the ability to, you know, threaten, harass, intimidate or fire them”.

Emboldened by a supreme court decision earlier this year that former presidents are entitled to some degree of immunity from criminal prosecution, Trump is “going to do some pretty amazing things that we’ve never seen before, and I think it’s going to be pretty horrible”, said Lenkart.

More than 1 million federal employees in the US are unionized, according to the Bureau of Labor Statistics, about half of the 2.1 million-strong civilian workforce in the federal government.

During his first administration, Trump chipped away at labor rights inside the federal government, shortening the time frame for collective bargaining, directing agencies not to bargain over certain issues, limiting the use of official work time for union business by federal employees and scaling back due process protections for employees.

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At federal agencies, unions expect such measures to return. Inside the National Labor Relations Board (NLRB) – the government agency tasked with enforcing federal labor laws and protecting the rights of workers across the US – the workforce is worried.

“Morale is about as low as it’s ever been,” said Michael Bilik, executive vice-president of the NLRB Union, which represents attorneys, investigators and administrative professionals in the agency’s field offices. It is already grappling with underfunding, staffing shortages and growing delays in processing cases, he said.

“I’m hearing questions, especially from new employees, like: ‘Should I be looking for another job?’ ‘Am I going to be the first to go since I was the last one hired?’” Bilik said. “I don’t think people fully understand the impact this could have, especially on smaller agencies like ours. It will further erode our day-to-day work resolving labor disputes, which benefits no one.”

Limiting official time for union matters will “strain labor relations” within the NLRB,” he added. “Our work will suffer, our union will be weakened, and the agency’s ability to function will be compromised if our staff and union are undermined.

“We’re in a very precarious position right now. Our backlog is skyrocketing, and we urgently need funding and personnel – not punitive restrictions on our basic ability to operate.”

AFGE Local 1003, which represents non-supervisory Environmental Protection Agency employees in Texas and surrounding states, is braced for a tough four years. During the first Trump administration, the union at the EPA was operating under an expired contract, and it only reached a new one this summer.

Under Trump, managers used a directive “which supplanted our expired contract at that time and caused a whole bunch of chaos, problems and headaches for the unions at the agency”, Justin Chen, president of AFGE Local 1003, said. “We couldn’t represent employees and grievances while on duty time. Essentially, they took away our offices and significantly shrunk our rights as the representation for the bargaining unit employees.”

Inside Trump World, there has been talk of replacing federal workers with “patriots” who live in communities nationwide. “We’re already out in these communities,” said Chen. “We’re just regular folks doing our jobs out over here as best as we can. We’ve often taken these positions because we have a love of our country.”