Colima has become the latest Mexican state to allow same-sex couples to enter into civil unions after a majority of local authorities passed a change in the state's constitution.
Legalisation on same-sex unions falls under state legislation, and a number of states have divergent rules.
Mexico City and the southern state of Quintana Roo allow gay marriages, while Coahuila allows same-sex civil unions.
Congress in Yucatan on the other hand banned same-sex marriage in 2009.
Seven out of ten authorities in Colima approved the constitutional change, which had been passed by the state's congress earlier this month.
Only two Congressmen voted against the change, arguing the state should legalise gay marriages rather than restricting same-sex couples to civil unions.
News of the change in the law in Colima came on the same day as Pope Francis told reporters that gay people should not be marginalised but integrated into society.
Speaking to reporters on a flight back from Brazil, the Pope reaffirmed the Roman Catholic Church's position that homosexual acts were sinful, but homosexual orientation was not.
Gay marriage was legalised in Uruguay earlier this year, and in Argentina in 2010.
In Brazil, the Supreme Court in May voted overwhelmingly in favour of allowing same-sex couples the same legal rights as married heterosexuals, effectively authorising gay marriage.
However, full legalisation of gay marriage in Brazil still depends on the passage of a law in Congress.