Opponents of the law that goes into effect on Jan. 1 said they have collected enough signatures for an initiative that would repeal it. Counties, however, were still reviewing the signatures.
The state previously said an early random sampling from counties via the secretary of state's office found only 77 percent of the signatures qualifying.
The coalition submitted 620,000 signatures to get the initiative on the November 2014 ballot, said Frank Schubert, political strategist handling the signature gathering effort.
To qualify, at least 505,000 valid signatures of registered voters must be verified through a random sampling. After that, it is likely the state would order a full review before the measure could be place on a ballot.
California is the first state to pass a law allowing such choices by transgender K-12 students.