A fifth AFL-CIO-affiliated group broke with the labor giant on Thursday to back former Labor Secretary Tom Perez over Rep. Keith Ellison (D-Minn.) in the race to be the next chairman of the Democratic National Committee (DNC).

The International Union of Bricklayers and Allied Craftworkers (BAC), which counts 80,000 members nationwide, said that as Labor secretary, Perez fought to implement a rule to limit worker exposure to a chemical compound that was causing debilitating and deadly diseases among the union’s members.

“It was Tom Perez who stood up to special interests and did what was right for workers across the nation by seeing this critical rulemaking to fruition,” BAC President James Boland said in a statement. “Tom understands the importance of good jobs, fair wages, and workplace protections that keep our members safe and healthy. Tom has stood beside us for tough fights before and we know he'll continue to do so as DNC chair.”

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BAC joins four other AFL-CIO-affiliated groups representing farm workers, firefighters, food and commercial workers, and plumbers and pipefitters in backing Perez.

The AFL-CIO as a whole, which represents 55 unions, has endorsed Ellison.

Even Perez’s allies concede that is a meaningful endorsement for the Minnesota Democrat.

However, it came with some controversy.

Only Ellison’s name was on the ballot that AFL-CIO President Richard Trumka sent to union members.

At the time, former DNC Chairman Howard Dean, New Hampshire Democratic Chairman Raymond Buckley and South Carolina Democratic Chairman Jaime Harrison were also in the race.

And Perez, who was the sitting Labor secretary, was expected to join soon.

Trumka’s move provoked a furious response from some labor leaders, who accused him of putting his thumb on the scale for Ellison.

Still, Ellison has picked up several key labor endorsements since then.

The culinary workers group Unite Here and the International Brotherhood of Electrical Workers are both backing him.

So is Perez's predecessor at the Labor Department, Hilda Solis, and the presidents of several other AFL-CIO-affiliated unions.