fCarnahan and Clay. (Photo/Post-Dispatch)

— Missouri’s largest group of labor unions is taking sides in the heated Democratic primary in the the state’s First Congressional District.

The Missouri AFL-CIO announced Wednesday that they are supporting incumbent Rep. Lacy Clay over his challenger Rep. Russ Carnahan.

“Organized labor is standing with Congressman Clay because he has always stood with us,” said Hugh McVey, president of the Missouri AFL-CIO. “In Congress, Lacy Clay has been a fearless defender of American jobs, American workers, and the right to organize and maintain a safe workplace.”

Clay also received support from the St. Louis Labor Council, a sign of potential frustration among Missouri Democrats over Carnahan’s decision to challenge Clay for reelection, after his former district was removed during redistricting.

“Organized labor is the heart of the Democratic Party. That’s why these endorsements are so powerful,” Clay said.

Missouri AFL-CIO also announced mostly symbolic endorsements of unchallenged incumbent Democrats like Gov. Jay Nixon and Sen. Claire McCaskill, as well as support for Jason Kander’s candidacy for secretary of state.

“Our state’s greatest asset is the highly skilled men and women who make the products and deliver the services that improve the lives of every Missourian,” said Kander.