Michigan Gov. Rick Snyder (R) will endorse Mitt Romney for president at a luncheon on Thursday, according to two sources with knowledge of his decision.

MIRS news reported Wednesday evening that the two men will appear together at a luncheon Thursday for a “major announcement.”

A source confirmed that Snyder will be endorsing the former Massachusetts governor, who is the early favorite in the Michigan Republican primary but may face a tough race against former Pennsylvania senator Rick Santorum.

Snyder is in his first term. He won an open seat race in a landslide in 2010 but has encountered some tough early sledding, and his approval rating has suffered some because of it.

Update: Snyder made his an endorsement official in a Detroit News editorial published Thursday.

“Mitt understands the challenges confronting Michigan as few Americans do,” Snyder wrote. “I hope all Michiganians will join me in supporting the candidacy of this favorite son of our great state.”