WASHINGTON — AFL-CIO boss Richard Trumka is using his political muscle to try to run interference for Hillary Rodham Clinton, after movement by some local labor groups to back rival Bernie Sanders.

The powerful union head advised state and local union chapters this week that the national union in DC handles presidential endorsements.

“I want to remind you all that the AFL-CIO endorsement for president and vice president belongs to the national AFL-CIO. State federations, central and area labor councils, and all other subordinate bodies must follow the national AFL-CIO endorsement,” Trumka wrote, according to Politico.

Clinton’s campaign is facing a growing challenge from Sanders. The South Carolina and Vermont AFL-CIOs passed resolutions this spring calling on “working people everywhere” to unite behind Sanders.