Mexico City (CNN) Same-sex marriage, already taking place in Mexico City and several other jurisdictions, would be legalized throughout the country under a plan Mexican President Enrique Peña Nieto proposed Tuesday.

The leader signed an initiative changing the country's Constitution, but he will need congressional approval for it to take effect.

"I signed reform initiatives to promote marriage equality (#MatrimonioIgualitario) and its addition to the Constitution and the Federal Civil Code," he tweeted.

Peña Nieto used the hashtag #SinHomofobia (without homophobia) on his official Twitter page and added a rainbow flag to his Twitter avatar.

Por un @Mexico incluyente que reconoce en la diversidad, una de sus mayores fortalezas #SinHomofobia. pic.twitter.com/6ooZGuPEsD — Enrique Peña Nieto (@EPN) May 17, 2016

Last year, Mexico's Supreme Court declared it unconstitutional for states to ban same-sex marriage.