The National Organization for Marriage has targeted Sen. Branden Petersen after he said last week he would support a bill to legalize same-sex marriage, the St. Paul Pioneer Press reported Tuesday.
NOM President Brian Brown said in a statement Monday Petersen's support for the bill would be "career ending."
The organization has pledged to spend $500,000 in the state to defeat any Republican lawmaker who votes for the bill.
"Regardless of the amount, whether it's $500,000 or $50 million, my vote is not going to be bought either way," Petersen said. "I'm going to do what's right."
Brown warned that NOM had worked to defeat four Republican senators in New York, and three of them were not re-elected.
Recent national statistics show that nearly all lawmakers who vote for gay marriage are returned to office, said Minnesotans United for All Families, which supports same-sex marriage.
Both houses of the Minnesota Legislature are expected to receive bills to legalize gay marriage this week.
Minnesota voters defeated a proposed constitutional amendment to ban gay marriage in November.