Love Honor Cherish will submit language to the California attorney general by Oct. 14 for a ballot measure to overturn Prop 8.
The attorney general will write a petition title and summary, and then LHC can collect voter signatures for 150 days.
The group would need to collect valid signatures from 807,615 registered California voters.
The initiative would amend the California Constitution to delete or overturn Prop 8, via which voters amended the Constitution in 2008 to re-ban same-sex marriage.
The Los-Angeles-based organization's outreach director, Lester Aponte, said Oct. 11 that LHC already has launched efforts to build a statewide campaign structure.
He also blasted Equality California for showing "a tremendous lack of leadership" when its board voted in early October against leading an effort to put Prop 8 back before California voters next year.
After the EQCA board vote, EQCA's new executive director, Roland Palencia, gave four days' notice that he was quitting his job.
Some California LGBT leaders think the EQCA board may reverse its decision.
EQCA has promised to provide information on its future leadership and plans before Palencia leaves on Oct. 14.
In a statement to this reporter Oct. 11, Palencia said: "The decision about going or not back to the ballot to overturn Proposition 8 was a gut-wrenching one. Ultimately, I believed that initiating a signature drive could ignite something powerful in our movement here in California. This needs to be balanced with the responsibility of raising close to $2 million by December 2011 for the signature gathering alone; and maybe over $40 million to win this campaign by November 2012. Not a small task. Given the pending federal lawsuit, the economy, critical support among the base and a number of other factors, not winning this campaign could be a very disempowering experience."