ASSOCIATED PRESS Sen. Bernie Sanders (I-Vt.) has picked up the endorsement of the postal workers union, which also backed him in the 2016 election.

Sen. Bernie Sanders (I-Vt.) added a major labor endorsement to his growing list Thursday, with the American Postal Workers Union throwing its support behind the Democratic hopeful.

APWU represents 220,000 postal employees and retirees across the country, adding to Sanders’ ground game in early primary states. The union also backed him in his failed bid for the Democratic nomination against Hillary Clinton in 2016.

The union’s president, Mark Dimondstein, said in a statement that there was plenty to like in the broader Democratic field, but that Sanders stood out for his long-time support of labor.

“We’re pleased that a number of presidential candidates have taken positions and actions supportive of postal workers and expanding union rights,” Dimondstein said. “But when we judge candidates by their long-term and consistent actions, Bernie Sanders stands out as a true champion of postal workers and all workers throughout the country.”

The postal workers’ announcement stands out from some of Sanders’ other recent labor endorsements in that it comes from a large national union, as opposed to a smaller local. Sanders, Sen. Elizabeth Warren (D-Mass.), former Vice President Joe Biden and other contenders are all competing fiercely for union support, which helps with door-knocking and phone-banking efforts in critical states.

Sanders has been an ally of APWU for years, often speaking out against steps by the U.S. Postal Service to reduce mail delivery or take steps toward privatization. Dimondstein said the union’s executive board cited that support in making their decision to support Sanders over the others.

The Vermont independent recently picked up the backing of one of the union’s affiliates, Iowa Postal Workers Union Local 44, in the critical caucus state. He also earned an endorsement from Service Employees International Union Local 1984 in New Hampshire.

On Tuesday, Unite Here Local 11 in California said it would be throwing its weight behind both Sanders and Warren for the nomination.