The director of California's largest gay rights group has said opponents of a gay history law would likely win if the law was put up for a vote.

California Governor Jerry Brown in July signed the measure which mandates the inclusion of the historical contributions of gay, lesbian, bisexual and transgender Americans in the state's textbooks.

Starting as early as the 2013-2014 school year, Senate Bill 48 or the FAIR Education Act, sponsored by state Senator Mark Leno, a Democrat, requires the California Board of Education and local school districts to include the curriculum in their lesson plans.

Opponents reacted swiftly, submitting ballot language to the state for a proposed referendum. The groups have until October 12 to collect the signatures of 504,760 registered voters to qualify for the next statewide ballot.

According The Bay Area Reporter, San Francisco's gay weekly, Equality California (EQCA) Executive Director Roland Palencia believes voters would repeal the law if given the opportunity.

“The prospects are not good if this gets to the ballot,” Palencia told reporters during a conference call. “I am not under any illusion.”

In statement released a few hours later, Palencia expanded on his comments: “We are realistic about how difficult this campaign will be, how hard it will be to win. But we also know that even if we start way behind, a loss is not a foregone conclusion. From our starting place our chances may not look good, but I don't believe it is impossible.”

In urging Governor Brown to veto the law, opponents called it an “attack on the family” and part of an agenda to indoctrinate children.

“Social engineering of homosexual, bisexual and transgender lifestyles is being done behind parents' backs. Most parents say no to this,” Randy Thomasson of the Christian conservative group Save California told Sacramento-based ABC affiliate News 10.