The National Treasury Employees Union threw its support behind former Secretary of State Hillary Clinton on Jan. 20, citing her record on labor issues.
"The 2016 election will have a huge impact on NTEU members and all federal employees," said NTEU president Tony Reardon, in a statement.
"This election will determine whether our country retains a talented and dedicated workforce with the necessary tools and resources to provide critical services to the American people. Secretary Clinton is a fighter who will ensure that federal employees and all working families get a fair shake and are treated with dignity and respect. I am proud to endorse her candidacy."
The endorsement marks another win for Clinton with federal employee unions, after picking up an endorsement from the American Federation of Government Employees in December.
NTEU noted that when Clinton served in the U.S. Senate, she earned a 96 percent on the union's scorecard.
Reardon said it was Clinton's history of support for federal workers and organized labor that help her win the union's pick.
"Throughout her career, Secretary Clinton has been a strong supporter of federal employees. I believe as president she will continue that support on issues from fair pay to protecting retirement benefits and workplace rights," he said. "Secretary Clinton recognizes the importance of the work done by federal employees and the need to recruit and retain a skilled federal workforce."
Clinton; Sen. Bernie Sanders, I-Vt.; and former Maryland Gov. Martin O'Malley are currently vying for the Democratic presidential nomination.