A Minnesota Republican who rebelled against her party to vote for same-sex marriage is in danger of being unseated by her former campaign manager.

Minnesota became the twelfth US state to allow equal marriage last year, after a bill passed through the heavily Democrat-controlled legislature.

Eden Prairie Representative Jenifer Loon was the most senior member of the Minnesota House of Representatives Republicans to vote for the bill in spite of her party’s stiff opposition.

According to the Sun-Observer, just four Republicans voted for the bill at the time, with one deciding not stand for re-election, and one ending his campaign early when facing a challenge.

Loon, who was deputy minority leader in the House, is now facing a closely-fought primary challenge from former campaign manager Sheila Kihne, in order to keep her seat.

The lawmaker won the district two years ago with 60% of the vote, but according to the newspaper “outside money” is rushing in to the race, to push out the pro-equal marriage Republican.

Kihne, who is painting herself as a ‘trusted conservative’ and is backed by the Minnesota Family Council, said of Loon’s vote: “It was a huge flip-flop and a big-time trust was broken.”

The election is set to take place on August 12.