The Traditional Values Coalition (TVC) is calling on Schwarzenegger to set the record straight over a 1977 interview in which the muscle bound actor discussed taking part in an orgy and using marijuana.
"We are very concerned about the report of Arnold's promiscuity and he must come forward and tell us if it stopped when he was 29, or if it continued," said the Reverend Louis Sheldon, head of the TVC.
California-based TVC touts itself as the largest non-denominational, grass-roots church lobby in America with a membership of about 43,000 churches, including most Christian denominations.
The TVC wrote about the controversy to 20 of the state assembly's 32 Republicans who have endorsed Schwarzenegger. He and 132 others are battling for the top job in the country’s richest state in an unprecedented recall vote on 7 October.
Schwarzenegger has been hounded in recent days by questions about the 1977 interview with the long-defunct men's magazine, Oui, in which he described his experiences with smoking marijuana and group sex when he was 29.
On Thursday, the actor-turned politician said he had "no idea what you are talking about" when asked at a news conference about the magazine interview.
"Is Arnold a Republican version of Bill Clinton?"
Traditional Values Coalition
But his spokesman Rob Stutzman on Saturday said the actor-turned politician "had been clear he had not lived his life in order to become the governor of California."
"Arnold was part of an industry 25 years, 30 years ago where it was common to say and do over-the-top, outrageous things," Stutzman said.
In its letter, the TVC asked: "Is Arnold a Republican version of Bill Clinton?", a reference to the former US president's sexual misbehaviour.
The TVC asked the Republican lawmakers "to consider holding off on persisting with your endorsement of Mr Schwarzenegger" until the candidate addressed the matter.
As a Republican, Schwarzenegger is trying to reach out to the party's powerful right wing, who might prefer a more conservative candidate like State Senator Tom McClintock, a long-time veteran of the California Legislature.
Polls show a majority of Californians would vote to recall Democratic Governor Gray Davis, who is unpopular because of his handling of the state's finances.
A recent Los Angeles Times survey found Democratic Lieutenant Governor Cruz Bustamante is in the lead to replace his boss – followed by Schwarzenegger.