The regional government of Isabel Diaz Ayuso has said that the People's Party will abstain in Thursday's voting at Madrid's regional parliament. But people took to the streets to express their support for LGBT rights.
The bill aims to abolish a regional law that guarantees the rights of LGBT people.
Among those protesting was Fran Rebollero, the spokesperson of a LGBT federation, who said he suffered a homophobic assault in the Spanish capital and later felt abandoned by regional police.
"I thought about what could have happened if I were alone rather than the fact that I was just assaulted. I thought about it in the next hours and the next day I reported to the national police because I felt not only assaulted but also abandoned by Madrid regional police," Rebollero said while at the protest.
Homophobic violence has been in the spotlight in Spain after the killing of nursing assistant Samuel Luiz, who was beaten to death in the northwestern region of Galicia in July allegedly because of his sexual orientation.
Spain was only the third country in the world to allow same-sex marriage in 2005.