Mexico's Supreme Court has rejected a bid to hold a national referendum on a major energy overhaul that opened the sector to widespread private investment for the first time in decades.

The court ruled Thursday that referendum petitions filed by two leftist parties are unconstitutional because matters of state revenue cannot be subjected to popular vote.

Energy reform's passage in August has been President Enrique Pena Nieto's biggest political victory since taking office in 2012.

It allows national and foreign private companies to invest in petroleum and electricity projects, something that was long considered taboo after oil was nationalized 76 years ago by then-President Lazaro Cardenas.

Mexico's political left strenuously opposed the reform and had sought to overturn it at the ballot box.