Opponents of California's gay history law have been cleared to begin collecting signatures for a ballot referendum to overturn the law.

On Tuesday, California Secretary of State Debra Bowen approved ballot language proposed by the Sacramento-based group Capitol Resources Institute, the AP reported.

California Governor Jerry Brown 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, 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, drafting their referendum's language in less than 2 weeks.

They must now collect the signatures of 504,760 registered voters by October 12 to quality for the next statewide ballot.

Supporters of the law say it will help ease the bullying gay teens face in the classroom.

Opponents have labeled it an attack on the family, and several have called on parents to remove their children from the public school system.

“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.

The Rev. Louis Sheldon, chairman and founder of the Traditional Values Coalition (TVC), said the measure “molested” the minds of children.

“It is an outrage that Governor Jerry Brown has opened the classroom door for homosexual activists to indoctrinate the minds of California's youth, since no factual materials would be allowed to be presented. By signing SB 48 today, California's classrooms, textbooks and instructional materials will all become pro-homosexual promotion tools.”

California's largest gay rights group, Equality California, said it would fight the referendum if it qualifies for the ballot.

“It's important for us right now to educate Californians about what the bill does and does not do,” Rebekah Orr, a spokeswoman for Equality California, told the AP. “We want to be clear that this bill is about teaching historical figures and not just LGBT people.”