MEXICO CITY - Mexico's foremost leftist leader predicted Sunday that protesters would prevent Congress from moving forward on the president's oil reform proposal during the current legislative session.
At a rally in Mexico City's central square, former presidential candidate Andres Manuel Lopez Obrador reiterated calls for a national debate on the reform bill.
President Felipe Calderon introduced it last week to allow state oil company Pemex to partner with private companies for oil exploration and refining.
Oil production in Mexico, one of the top suppliers to the United States, is declining, and reform advocates say Pemex needs outside resources to explore for more reserves.
Legislators from Lopez Obrador's Democratic Revolution Party and two minor parties have camped out around the clock in both chambers of Mexico's Congress to block discussions on the bill.
Congressional leaders have said they might look for a new place to conduct legislative business.
"It's almost certain that they won't be able to approve the sellout initiatives before the end of this congressional session on April 30," Lopez Obrador told more than 100,000 supporters who packed the Zocalo.
Mexico's constitution bans most private and foreign involvement in the industry, although Pemex subcontracts some work to private firms. The bill would allow Pemex to pay bonuses to private companies but not a share of the oil profits.
Lopez Obrador said the bill aims to privatize Pemex, allowing Mexico's oil revenues - which now account for nearly 40 per cent of the national budget - to go to private and foreign companies.
He urged his followers to go house by house and neighbourhood by neighbourhood to educate Mexicans about "the grave consequences" of the bill.
Lopez Obrador narrowly lost the presidency to Calderon in 2006 and blames fraud for his defeat.
He has since refused to recognize Calderon's government.