A coalition of conservative groups called Privacy for all Students submitted 620,000 signatures to get the initiative on the November 2014 ballot, said Frank Schubert, the political strategist handling the signature gathering effort.
To qualify, at least 505,000 valid signatures must be submitted. To verify the signatures, each of California's 58 counties will first check that the overall count is correct, then conduct a random sampling to make sure they are legitimate. After that, it is likely the state would order a full review.
If, after all of the reviews, the group has the requisite number of valid signatures, the initiative would qualify for the ballot.
"Many people said we had no chance to collect over half a million signatures in just 90 days, but we have proven them wrong by gathering over 115,000 more signatures than the minimum needed," Gina Gleason of the group Faith and Public Policy, said in a statement.
California is the first state to pass a law detailing the rights of transgender K-12 students.
One of the provisions gives transgender students the choice of playing on either boys or girls sports teams. It also allows them to choose which restroom that want to use.
Gov. Jerry Brown signed the law, AB1266, in September. It goes into effect Jan. 1.
The goal of the law is to reduce discrimination against transgender students.
John O'Connor, executive director of Equality California, the organization that co-sponsored the transgender student law, said he was alarmed by the initiative effort.
"Protecting this law is our number one priority, and we will put everything we've got into it," O'Connor said, adding that he believes public opinion is opposed to discrimination against LGBT people.
The effort to repeal the law got a boost last month when the National Organization for Marriage, which organized the 2008 ballot initiative that outlawed gay marriage in California, joined the effort.
Schubert, who helped organize the signature push, previously led successful campaigns to block same-sex marriage in Maine and North Carolina.
Supporters of the repeal effort argue the law violates the privacy of non-transgender students.
They said 400,000 of the signatures gathered were done by volunteers, as opposed to 220,000 collected by paid staff.
"It shows the degree of opposition that exists to opening the most vulnerable areas of public schools to the opposite sex," Karen England of Capitol Resources Institute, a coalition member, said in a statement.