The Pacific Justice Institute, a Christian law firm, is challenging California election officials over a petition to vote on the state's co-ed bathroom bill.
The controversial law allows transgender students to use bathrooms and locker rooms of the opposite gender.
Secretary of State Debra Bowen disqualified 131,000 signatures on the petition calling for a state-wide referendum on the measure.
Now the Pacific Justice Institute is filing suit for Bowen to certify the referendum for the November 2014 ballot.
It alleges the reasons Bowen gave for throwing out the signatures are subjective and vary from county to county.
Last November, Bowen tried to block hundreds of thousands of signatures from being counted.