AUGUSTA — The founder of a constitutional rights group that opposed same-sex marriage in Maine said Monday that he plans to challenge U.S. Sen. Susan Collins in the Republican primary next year.

Erick Bennett said he tried unsuccessfully to recruit others to run against Collins, a three-term incumbent who has carved out a reputation as a moderate Republican. So Bennett said he agreed to run against her in the Republican primary.

“Unless she has a challenger, people are not going to have a choice. And unless there is a choice, people are not going to know what they are getting,” said Bennett, a Portland resident who ran as a write-in candidate for mayor in 2011.

Bennett is the founder of the Maine Equal Rights Center, a conservative group that formed last year to oppose the successful ballot initiative that legalized same-sex marriage in the state. Bennett labeled gay marriage as “communism” and predicted the practice would “legalize discrimination.”

His group is now trying to gather signatures for three referendum campaigns in 2014: to nullify the national Common Core educational standards in Maine; to eliminate Maine’s concealed handgun permit requirement; and to require parental consent for abortions on girls age 16 and under.

While some polls have suggested that Collins could be vulnerable to a more conservative primary opponent, Bennett would face a difficult road as a little-known challenger to an incumbent senator with more than $2 million in her campaign account.

Shenna Bellows, the former executive director of the American Civil Liberties Union of Maine, is running against Collins on the Democratic ticket.

Collins’ office did not immediately return a call seeking comment on the potential primary challenger.

Kevin Miller can be contacted at 317-6256 or at:

kmiller@pressherald.com

Twitter: @KevinMillerDC