The Mexican Senate approved legislation early Wednesday to overhaul the country's energy industry, a historic move that will open the sector to private investment.

Lawmakers must still debate some points in the bill that are being challenged by leftist legislators.

The bill, which was backed by the President Enrique Peña Nieto's Institutional Revolutionary Party, or PRI, and the conservative National Action Party, or PAN, was approved on a vote of 95-28, Senate spokesmen said.

The bill modifies Articles 25, 27 and 28 of the Mexican Constitution in response to the "historic responsibility of turning the energy sector into the lever for national development," a statement by the PRI said.

The senate session, which started at 2:30 p.m. on Tuesday, continued after the vote to approve the general terms of the bill, with senators expected to debate other points of the legislation on Wednesday.

The bill calls for ending the monopoly on petroleum production currently held by state-owned oil giant Petroleos Mexicanos, or Pemex, and allowing private companies to enter into profit- and production-sharing contracts with the government.

Once the bill is fully approved by the Senate, it must be approved by the lower house of Congress and at least 17 of Mexico's 32 state legislatures.

The leftist Party of the Democratic Revolution, or PRD, opposes opening the energy industry to private investment and wants to hold a referendum in 2015 to scuttle the legislation.

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