By Ariel Crespo CNN

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.

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

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

Mexico City legalized same-sex marriages and adoptions in 2009.

Lawmakers in eight of Mexico's 32 states or jurisdictions have approved same-sex marriage. In addition to Mexico City: Campeche, Jalisco, Coahuila, Quintana Roo, Colima, Nayarit and Chihuahua.

Mexico's secretary of finance and public credit tweeted, "Why fight?" with a rainbow background.

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