“Whether it’s a unit that’s represented by a labor organization or not, the process is fairly onerous,” said David Cann, American Federation of Government Employees director of field services and education. “These things are being discussed rashly with no consideration of how long it takes to accomplish it. It shouldn’t take a year but it can.”

He added: “If it is done improperly, people can appeal it and get their job back and get back pay. It can be expensive. And inefficient.”

There are additional realities. Congress, which ultimately holds the power to pass the budget for the year beginning Oct. 1, 2017, may not be so cooperative; early reaction Thursday to Trump’s budget was not enthusiastic, even among Republicans.

And agencies typically are given broad flexibility to manage their own budgets. Programs under the budget ax can look first to reducing travel, training and office equipment purchases. Instead of laying off employees, they can put them on temporary unpaid furloughs — time off without pay — as many did in response to across-the-board budget cuts imposed in 2013.

In the past, agencies have often looked first to attrition. The Trump administration already has put the first such step in place, imposing a general hiring freeze on the federal workforce — with exceptions for positions involving national security or public safety. That same action called for the administration to produce a separate long-term plan to reduce the workforce by attrition.

Neal said that normal attrition in the federal workforce is unlikely to achieve the massive reductions that Trump proposes — and certainly not within the fiscal year starting in October. Turnover doesn’t always take place where agencies want it to happen, he added.

Mick Mulvaney, the director of the Office of Management and Budget, said the depth of the cuts required at many agencies would make it very difficult to avoid lay-offs. “I can’t imagine how you’d take some of these reductions and don’t have a reduction in the workforce, which is exactly what the president talked about,” Mulvaney said.

However, he added: “We gave a great deal of flexibility to the secretaries and the agency directors. So how they manage that would be up to them on sort of a case-by-case basis.”

Trump’s budget blueprint is sparse on explaining how spending reductions might translate into job cuts.

Reducing an agency’s budget by a certain percentage does not necessarily mean the workforce would be cut by that same amount. That’s especially the case with agencies that devote much of their spending to contracts and grants, such as the Department of Health and Human Services and the Department of Housing and Urban Development, in contrast to agencies that are more labor-intensive per dollar, such as the Department of Labor.

As of September, there were 2.096 million total executive branch employees, not including the intelligence community and the self-funding U.S. Postal Service, according to an Office of Personnel Management database.

Excluding temporary, seasonal and part-time employees puts the number at 1.867 million.

One scenario in which programs would be compelled to go through the RIF process: If the entire agency is being shut down. The Trump administration budget proposes shuttering 19 independent agencies, mostly small boards and commissions, along with several sub-agencies of Cabinet departments.

The one agency workforce the budget specifically targets is the Environmental Protection Agency, where an overall spending reduction of 31 percent “would result in approximately 3,200 fewer positions at the agency” — about a 20 percent reduction of a workforce of about 15,600.

“You can’t drain the swamp and leave all the people in it. So I guess the first place that comes to mind will be the Environmental Protection Agency — that the president wants a smaller EPA. He thinks they overreach, and the budget reflects that,” Mulvaney said.

Other agencies facing substantial cuts include the Departments of State, Agriculture, Labor and Health and Human Services. Further reductions could lie ahead due to a recently issued executive order calling for a government-wide reorganization to make agencies more efficient, with a formal proposal expected in about a year.

However, budgets have to go through Congress. Even some elements of the upcoming reorganization plan would require Capitol Hill’s approval.