Michigan Sen. Carl Levin's decision not to seek reelection gives Republicans an unexpected opportunity to challenge for the long-held Democratic seat with a solid field that includes several House members and perhaps another Romney.

The six-term senator made the announcement Thursday, sparking interests from Republican Reps. Dave Camp and Mike Rogers.

Scott Romney, brother of 2012 Republican presidential nominee Mitt Romney, also is interested in joining the 2014 race, a state Republican source has told two news-gathering agencies.

Romney is a Harvard Law School graduate who works at the Detroit firm of Honigman Miller Schwartz and Cohn LLP.

Earlier this year, Mitt Romney’s wife, Ann, and son Tagg were mentioned as potential Republican candidates for Massachusetts Sen. John Kerry’s open seat when former Sen. Scott Brown, R-Mass., deciding not to run.

Levin said in his announcement that he can best serve Michigan and the country by spending the final two years of his term focused on key issues facing Congress.

“In other words, by doing my job without the distraction of campaigning for re-election,” he said.

On the Democrats side, Reps. Gary Peters and Dan Kildee are also considering a run.

Peters said Friday that he was "very interested" in running and that Democrats holding that seat is “absolutely critical.”

The seat has not been closely contested since 1984.

Other Democrats interested in running include national committeewoman Debbie Dingell, the wife of long-time Rep. John Dingell, and University of Michigan regent Mark Bernstein.

Another potential Republican candidate is Michigan Rep. Justin Amash. He is the second-term conservative adored by Tea Party groups but removed from a committee assignment in December after casting votes defying party leadership. If Amash won the primary, some Republicans worry he would not appeal to independent voters in the general election.

He tweeted Friday that the state Republican Party "cannot put up an unelectable establishment candidate for Senate who doesn't appeal to independent & moderate voters on federal issues."

Republican and former two-term Secretary of State Terri Lynn Land, who previously considered running against Democrat Debbie Stabenow, the state’s junior senator, is also considering a run.

Levin's departure puts Democrats at a disadvantage as they already are looking for someone to challenge Republican Gov. Rick Snyder and to retake control of the Republican-dominated state government. But Democrats also have fared well in federal elections in a state that has gone for Democrats in six straight presidential races.

 Just one Republican has won a Michigan Senate seat in 40 years, Spencer Abraham in 1994, a non-presidential year like 2014 will be. The last close race was in 2000, when Stabenow defeated Abraham.

"It's a tremendous opportunity for Republicans. This is like a once-in-decades opportunity," said Stu Sandler, a state Republican consultant. "There's a pretty strong bench out there."

The Associated Press contributed to this story.