WASHINGTON — Congress is nearing a deal on paid parental leave for federal employees, according to four sources familiar with the negotiations. It's a significant development for government workers but one that highlights the disparity with most American workers, who still aren’t given paid leave.

The agreement would give 2.1 million non-military federal workers 12 weeks of paid leave to care for a newborn or adopted child or to care for a family member, according to sources familiar with the details of the discussions. If passed, the bill would the become first time the federal government has guaranteed civilian employees access to paid parental leave.

The federal workforce is part of the 83 percent of workers in the nation who aren’t provided any paid family leave, including parental leave, according to the Bureau of Labor Statistics. While the Family and Medical Leave Act provides 12 weeks of leave to care for a child or ailing family member, none of that is guaranteed to be paid, and the unpaid time off is often too much of a financial burden to use for many families.

The measure was negotiated as part of the National Defense Authorization Act, an annual bill that sets defense priorities. It was included in the version of the defense bill that passed the House, but its fate remained uncertain when negotiations with reluctant Republicans began in the Senate. After more than three months of negotiations, it was one of the last issues to be dealt with. The NDAA still must pass both houses of Congress before it reaches the president's desk.

Democrats are applauding the move. Sen. Brian Schatz, D-Hawaii, said the deal, if enacted, would be a big win since the federal government is the nation’s largest employer.

“If this is enacted, it will mean that public servants won’t have to make the impossible choice of getting a paycheck or taking care of their children,” Schatz told NBC News.

Sen. Kirsten Gillibrand, D-N.Y., called it a “huge step.”

“This means that the largest employer in the country now provides basic parental leave, a huge step, and we must work to ensure that paid leave for other family emergencies will be added in the future.” Gillibrand said.

Rep. Carolyn Maloney, D-N.Y., who has championed this issue, is slated to hold her first hearing as chair of the House Oversight and Reform Committee on national paid and family leave on Tuesday.

A large majority of Americans support paid family leave but disagree on whether the government should require it or help to subsidize it. The United States is the only developed country without paid leave for new mothers.