BOSTON (STATE HOUSE NEWS SERVICE) – Opponents of the transgender public accommodations bill that Gov. Charlie Baker signed into law just over a week ago announced Monday they have launched a referendum initiative to repeal the law in 2018.

Led by the Massachusetts Family Institute, which largely organized the opposition to the bill, 21 people on Monday filed a referendum petition with the Secretary of State’s office to initiate the repeal process for 2018. The bill became law too late for the repeal effort to make it onto the 2016 ballot.

“Over the next 80 days, more than 32,000 signatures will need to be collected to put the transgender bathroom, locker room and shower law on the ballot in November 2018,” MFI wrote in an email to supporters. “This will be a long process, not only of getting the repeal question on the ballot, but of continuing to raise awareness about the problems that laws like this are causing all over the country.”

A referendum petition to repeal a law requires 32,375 signatures, less than half the number of certified signatures than does a ballot initiative that would create a new law.

Signed by Baker on July 8, the bill (S 2407) bans discrimination based on gender identity in places of public accommodations and would allow transgender people to use sex-segregated facilities, like locker rooms and bathrooms, that correspond to their gender identity rather than anatomical sex.

The bill directs the Massachusetts Commission Against Discrimination to adopt policies on enforcing the law and also requires the Attorney General’s office to provide guidance on how to handle legal action if any person were to assert gender identity for an improper purpose. Both offices have until Sept. 1 to report their recommendations, with the law taking full effect on Oct. 1.

MFI opposed the bill, arguing that it would compromise the privacy and safety of women and children, and prevent parents from protecting their children from men who claim to identify as female simply to gain access to a women’s bathroom or locker room.