Hillary Clinton has received yet another blessing from organized labor. On Thursday, the 670,000-member American Federation of Government Employees (AFGE) -- the largest union representing federal workers -- announced its endorsement of the former secretary of state for president.

“AFGE needs to make sure that whoever occupies the White House values our work and our agencies' mission to serve the public,” the union said in a statement. “We need someone with the spine to stand strong against the anti-government ideologues that want to shut down the government and eliminate your jobs.”

The move bolsters Clinton’s ongoing efforts to shake off an unexpected challenge from her chief opponent in the Democratic primaries, Sen. Bernie Sanders of Vermont. AFGE’s nod adds to her impressive collection of labor union endorsements, which now include the largest public employees’ union, the powerful service workers’ union, the two largest teachers’ unions and several building trades unions -- groups that together represent nearly two-thirds of the country’s unionized workforce.

Sanders is seen by many union leaders as a strong supporter of the labor movement but also less likely to win the Democratic nomination -- and the general election -- than the former first lady. Despite well-publicized lobbying efforts from members who support Sanders, few unions have given official backing to the self-described socialist -- most notably, National Nurses United and the American Postal Workers Union.

While the share of American workers who belong to unions has declined substantially over the past few decades, labor unions remain a significant force in electoral politics. Endorsements are often coveted by candidates because they can translate into hefty campaign contributions and critical get-out-the-vote support.

The nation’s largest labor federation, the AFL-CIO, has yet to make a presidential endorsement. Historically, it has waited until after the close of the competitive primary season to do so.