WASHINGTON (AP) — Federal employee labor unions are trying to soften the blow for more than 1 million government workers who may be forced to take unpaid time off if mandatory budget cuts kick in this week.

Union leaders have been working furiously to persuade agency managers to make other cuts that won't affect employee paychecks. But if agencies do insist on furloughs, unions say they can bargain over when they take place and other terms that could help workers in financial trouble.

"We plan to exercise those rights," said Jacqueline Simon, public policy director at the American Federation of Government Employees, which represents over 650,000 workers.

More than half of the nation's 2.1 million government workers may be required to take furloughs if automatic budget cuts, known as the sequester, take effect and agencies are forced to trim budgets. Agencies also may impose hiring freezes, release temporary employees or decline to renew contract workers.

The Defense Department has said it expects to furlough 800,000 civilian workers for 22 days each, spread across more than five months, which would mean a 20 percent pay cut over that period. The Pentagon also plans to lay off as many as 46,000 temporary and contract employees.

Other federal agencies are likely to furlough several hundred thousand more workers, according to a memo last month from the Office of Management and Budget.

Unions can't stop furloughs, but they can ask to examine the agency's budget documents and make managers show there is no other way to make the cuts without furloughs.

"Our position is that the Department of Defense and every other agency actually has a lot more discretion than they're letting on and that furloughs are entirely unnecessary," Simon said. "There's certainly plenty of low-paid federal employees for whom a 20 percent pay cut means they will not be able to pay their bills."

Besides receiving no pay, a worker on furlough would not accumulate vacation time and would receive a smaller match for their government retirement account. The worker's annual salary also would be lower when calculating pension benefits.

"The impact is going to be devastating, not just on the employees who are serving unpaid furlough days, but on the American public, who depend on the services these employees provide," said Colleen Kelly, president of the National Treasury Employees Union, which represents about 150,000 workers at 31 federal agencies.

So far, Kelly's union has received only one official notice of intent to furlough workers. That came from U.S. Customs and Border Protection, which plans to furlough all 60,000 employees for up to 14 days if the sequestration goes into effect. Kelly said other agencies are looking at furloughs but have not yet specified the cuts.

"We've reached out to agencies in an effort to work with them to find ways to cut spending so that the cuts don't come on the backs of employees on furlough days," she said.

The general expectation is that employees would serve one furlough day per two-week pay period. But the union can bargain on behalf of employees who may want to serve all the days together or delay them until later in the year for personal or financial reasons.

Negotiations can also resolve whether workers can swap furlough days with other employees, or whether some workers can volunteer to serve more furlough days so others don't have to. There also may be work deadlines to consider, since some workers remain accountable to complete projects even if they cannot be at work.

The federal Office of Personnel Management, which issues guidance on how agencies carry out furloughs, declined a request for comment. But in a memo to agencies, OPM states that government officials have duty to bargain "over any negotiable impact and implementation proposals" the union may submit regarding furloughs.

In a memo to Environmental Protection Agency employees on Tuesday, acting administrator Bob Perciasepe said the agency has been taking "aggressive action" to control costs over the past few months, such as reducing contract, grant and administrative spending. But even with those savings, he said, the EPA would still have to furlough workers.

"We are working to minimize the burden on employees and their families while still enabling the agency to meet its obligations and fulfill its mission," Perciasepe said. "We are also meeting with EPA's national unions to prepare a plan for implementation."

Every agency must provide notice at least 30 days before any furlough process begins. The earliest furloughs could begin is April 1.

A few agencies have said they expect to avoid furloughs, including the Social Security Administration, Small Business Administration and Smithsonian Institution. The Veterans Affairs Department has been excluded from sequestration cuts.

"Agencies can be creative and agencies can be uncreative," Simon said. "Our position is, don't come to us because we're the easy target."