MEXICO CITY (AP) -- Leftist presidential candidate Andres Manuel Lopez Obrador and his party formally filed a petition Thursday asking Mexico's electoral court to invalidate the results of the July 1 presidential ballot, charging there was vote buying and campaign overspending by the winner of official vote counts.
Lopez Obrador's campaign coordinator, Ricardo Monreal, and Jesus Zambrano, president of the Democratic Revolution Party, turned in the petition along with at least 20 boxes containing alleged proof of vote-buying by members of the Institutional Revolutionary Party, or PRI.
The court has until early September to deal with any challenges and determine whether to validate the presidential election in which the PRI's candidate, Enrique Pena Nieto, finished first with just over 38 percent of the votes.
Lopez Obrador also said that next week he will reveal what he called "a national plan in defense of democracy and Mexico's dignity."
He didn't give any hints on what the plan would entail, but said he and his supporters would act peacefully.
"I call on all Mexicans not to allow the shameless violation of the constitution," Lopez Obrador said. "We will always act peacefully; we won't give them any excuses to accuse us of being violent."
The announcement comes amid rising calls to investigate what appears to have been the distribution of thousands of pre-paid gift cards to voters before the election, and allegations by Lopez Obrador's supporters that some PRI state government officials passed funds to Pena Nieto's campaign effort.
Lopez Obrador also said that Pena Nieto was favored by Mexico's television broadcasters and that pre-election polls were used as propaganda to confuse people.
Most polls consistently put Pena Nieto as the front-runner, often showing him leading by double-digits over Lopez Obrador. However, the vote count gave him only a six-point victory over Lopez Obrador.
"In a free election the majority of those citizens would not have voted for Enrique Pena Nieto," Lopez Obrador said.