Tens of thousands of people rallied against President Enrique Pena Nieto\'s economic reforms in Mexico\'s capital Sunday, with leftist leader Andres Manuel Lopez Obrador calling for peaceful resistance. Mexico City police said more than 40,000 people gathered in a park to reject plans by Pena Nieto to overhaul the tax system and open the country\'s state-controlled oil industry to foreign investors. \"We can prevent the privatization of the energy sector and the tax increases through peaceful citizen mobilization,\" said Lopez Obrador, who never recognized his defeat to Pena Nieto in the 2012 presidential election after claiming fraud. \"These energy and tax reforms were prepared abroad for the benefit of foreign companies, a commitment that Pena Nieto made with foreign companies in the United States and Britain,\" he said, calling for another rally on September 22. He called the oil reform a \"vile and shameful robbery.\" Lopez Obrador made his plea as Pena Nieto prepared to present a revamp of the tax system to increase the government\'s revenue stream amid reports that he may propose a controversial sales tax for food and medicine. The Mexican president, who took office in December, has struck a pact with rival leftist and conservative parties that has secured telecommunications and education reforms despite protests by teachers. Last Monday, he defended his reforms and urged Mexicans to back the \"grand transformation\" of the country, stressing that the overhaul was necessary to improve education, create jobs and improve a slowing economy. Pena Nieto says the energy shifts aim to allow private firms to enter into profit-sharing agreements with state-run giant Pemex to modernize the company, but he denies plans to privatize an industry that was nationalized 75 years ago. Speaking on a stage in front of a giant banner that read \"No to the biggest robbery of all time,\" Lopez Obrador said the tax overhaul will dig into the pockets of ordinary Mexicans to make up for losing Pemex profits. \"Oil is the engine, the fuel of our society. It\'s an essential and profitable product that belongs to society,\" said Alberto Castro Gonzalez, a 45-year-old teacher wearing a poster of a barrel of oil with the words \"Mexico is not for sale.\" \"They want to sell it, but the government is our employee. We, the Mexican people, are the owners,\" he said. Lopez Obrador had planned to hold the rally in front of the National Palace at the historic Zocalo square, but he was forced to move it to the park because thousands of teachers have been camping out there for the past three weeks. With Pena Nieto having a deal with rival parties to pass the reforms in Congress, Lopez Obrador said: \"The only thing that can stop these measures, which are contrary to the nation\'s interests, is citizens mobilizing.\" But despite holding several protests that have disrupted life in the metropolis of 20 million people in the past three weeks, the teachers ultimately failed to block Pena Nieto\'s education reform.