The ethics commission today rejected a request from the National Organization for Marriage to end an investigation of the group’s finances.

 The group, which was the biggest contributor to the successful Yes on 1 campaign to repeal the state’s same-sex marriage law, argued in a letter to the commission that it did not have the legal power to conduct an investigation.

 But on a 4-0 vote this morning, the commission rejected that argument.

 “It seems to me if this was such a compelling issue for them they would have brought it earlier,” said Commission Chairman Walter McKee. “I have no doubt this will be appealed to Superior Court.”

 Last October, the commission voted to have staff investigate the fund-raising tactics used by the group. That investigation has been stalled by legal challenges in both state and federal court.