(CNN) – The coalition of conservative groups behind the "Cut, Cup and Balance" pledge to oppose a debt ceiling hike without major spending cuts and a balanced budget amendment is pressuring Republican presidential candidates Mitt Romney, Michele Bachmann and Jon Huntsman to get on board.

Huntsman, the former Utah governor, has already said he does not plan to sign the pledge, which has the backing of more than 150 tea party and conservative groups. A dozen Republican senators and 20 House members are also on board.

One of those senators, South Carolina's Jim DeMint, told CNN over the weekend that the pledge is a litmus test for his support said he has ruled out backing Huntsman's bid as a result.