Thousands of people fill Mexico City's Paseo de la Reforma during a gay pride march on June 30, 2012.

MEXICO CITY – Mexico's Supreme Court has ruled that a law in southern Oaxaca state that bans same-sex marriages is unconstitutional, paving the way for same-sex couples to marry in that state and possibly in the rest of Mexico.

In a unanimous decision on Wednesday, the tribunal struck down a Oaxaca state law that declares that "one of the purposes of marriage is the perpetuation of the species."

The court said in its ruling that to condition marriages to the union of one man and one woman "violates the principle of equality."

Currently, same-sex marriage is only legally allowed in Mexico City, where a same-sex marriage law was enacted in 2010.

The court's ruling comes from a lawsuit filed by three gay couples against the state of Oaxaca.