Budget director Mick Mulvaney speaks during a budget briefing at the White House in February. (Alex Wong/Getty Images)

Even as the White House lifts a freeze on government hiring, it’s telling most federal agencies not to resume filling jobs and instead to shrink their staffs.

They have a stockpile of tools to get started right now.

Federal leaders can decide on their own to offer buyouts and early retirement packages to their employees. They can even begin the long process of laying them off, citing agency “restructuring” as the reason. They can eliminate vacant positions altogether, or redraw their organization charts so that lower-level, lower-paid employees do the work done by higher-paid ones.

Congress does not need to sign off on these particular strategies to reduce the federal workforce, according to federal budget and personnel experts. That’s why Office of Management and Budget Director Mick Mulvaney instructed agency heads Wednesday to move quickly to carry out President Trump’s campaign pledge to “drain the swamp” by reining in the federal bureaucracy.

If agencies have the money to offer buyouts or lay off employees, they can proceed — although they need to notify Congress and get a rubber stamp from the Office of Personnel Management. The terms of some staff reductions would need to be negotiated with federal employee unions.

“Agencies can do a lot to reorganize themselves to do things differently,” said Jeffrey Neal, a former chief human capital officer for the Department of Homeland Security who is now a senior vice president at ICF. “They are the executive branch and they get to execute.”

The White House also is instructing agencies — with the exception of Defense, Veterans Affairs and parts of Homeland Security, which Trump wants to give additional money — to craft by June 30 long-term plans to slash their staffs over several years starting in October 2018.

The agencies are supposed to use as guidelines a spending plan Trump released in March for the next fiscal year. The budget blueprint calls for drastic cuts to many agencies, including the State Department and the Environmental Protection Agency, and the elimination of dozens of small programs altogether. The potential cuts are hurting morale in federal offices across the country as employees brace for the worst.

The budget is where the administration’s plans to reshape the government could run into trouble, experts say.

Congress decides how federal agencies are funded, and the president’s “skinny budget” has received a bipartisan thumbs down on Capitol Hill.

Mulvaney told reporters this week he’s confident that lawmakers eventually will support the proposal, saying, “I think they probably are as interested — they’re frustrated as everybody else is, as every other citizen is, as to how poorly the federal government can function, how inefficient it is.”

A looming question, though, is what the administration will do if Congress funds programs that Trump wants to get rid of — and what legal authority the White House would have to keep shrinking the government in that case.

Here’s some history. After President Richard M. Nixon opposed a number of programs in spending bills passed by a Democratic-controlled Congress in 1974 — and threatened to prevent agencies from spending some of the money lawmakers gave them — Congress passed legislation to limit a president’s power in this part of the budget process.

Today, it’s almost impossible for a president to decide not to spend money that Congress appropriated, although the chief executive can defer spending “to achieve savings through more efficient operations.”

Does the law limit the president’s authority to staff those operations? That’s unclear, experts say.

Spending bills typically allocate money for a specific agency’s salaries and expenses. Agencies usually wants more money to pay for their operations, though, not less.

“Did [Congress] give the administrator of an agency enough flexibility to say, ‘You can manage your employees any way you want and still accomplish the objectives of the agency?’” asked Bill Hoagland, senior vice president at the Bipartisan Policy Center and a former budget adviser to a long line of Senate Republican leaders.

“Some people in Congress will say, ‘Those employees are there to carry out a particular function, and you’re jeopardizing the number of people who are needed to process Social Security checks,’” Hoagland said. “Then we’ll have a big debate.”

What can Trump really do to reduce the federal workforce if Congress disagrees?

“It’s terribly murky,” Hoagland said.

Scott Lilly, a senior fellow and budget expert at the Center for American Progress, said the budget law is clearer to him.

“Mulvaney can’t take actions that require funds not to be expended,” Lilly said of the budget director. “He would have no business taking executive actions that would emasculate programs in the absence of congressional action.”

Lilly noted that presidents from Ronald Reagan to Barack Obama have pledged to consolidate and eliminate federal agencies to varying degrees. “In the end, the cuts were relatively modest.”

On Wednesday, Congressional Republicans praised the White House effort to restructure the government. Democrats and federal employee unions said the administration is threatening the missions of many agencies and opening the door to outsourcing too much work for private companies.

House Majority Leader Kevin McCarthy (R-Calif.) said in a statement that he supports the effort to “review the massive web of federal bureaucracy,” although he did not address the workforce directly.

Senate Minority Leader Charles E. Schumer (D-N.Y.) said in a statement, “Any proposal from OMB Director Mulvaney or the administration that eviscerates the very agencies and employees dedicated to helping the middle class … will be met with strong opposition by Democrats in Congress.”

Rep. Elijah E. Cummings (Md.), the top Democrat on the Oversight and Government Reform Committee, whose suburban district includes thousands of federal employees, urged Trump to “reconsider” what he called “massive staffing cuts.”

Spokesmen for several federal agencies did not respond to requests for comment on how they plan to carry out the White House’s order. But Interior Secretary Ryan Zinke said he intends to approach it this way:

“Empower the front lines, cut the waste, fraud and abuse, hold people accountable, and do more with less,” he said in a statement.

“I won’t be afraid to make investments where appropriate.”

Read more:

Trump wants to give federal workers a raise

Trump has a plan for federal workers. They’re not going to like it.

Bobbleheads, yes. Official tweets, no. Federal workers wonder where the lines are in the age of Trump