The runner-up in Mexico's presidential race on Thursday filed suit before the country's electoral court in a bid to void the results on charges the winner broke campaign finance laws and bought millions of votes.
Left-wing candidate Andres Manuel Lopez Obrador came in 3.3 million votes behind Enrique Pena Nieto from the centrist Institutional Revolutionary Party (PRI), according to the official count from the July 1 vote.
But the former mayor of Mexico City, who lost the 2006 presidential race by a narrower margin, says the campaign was rigged, with major media outlets skewing coverage to promote the telegenic Pena Nieto at the expense of the other parties.
Lopez Obrador said he had proof Pena Nieto enlisted help from local governors to buy around 5 million votes by doling out pre-paid gift cards, cash, foodstuffs, building materials and fertilizer to lure poor voters to the ballot boxes.
"The massive vote buying operation was carried out before and on the day of the election," Lopez Obrador told a news conference, adding he would next week unveil a "national plan for the defense of democracy and the dignity of Mexico."
In 2006, Lopez Obrador also refused to accept his loss to President Felipe Calderon by less than 1 percentage point. Financial markets were rattled when his supporters staged weeks of disruptive protests, occupying the capital's main boulevard.
This time markets have largely shrugged off the possibility of a drawn-out conflict and Pena Nieto is already naming advisers to work on his government's transition.
Lopez Obrador stopped short of calling for protests and said his camp will argue before the electoral tribunal, known as the TRIFE, that the PRI broke the rules for free elections.
His lawyers filed their complaint with election officials Thursday evening, delivering dozens of boxes filled with documents, videos, photos as well as home appliances, clothes and kitchen utensils allegedly given away by the PRI campaign.
The TRIFE has until Sept. 6 to consider all claims and officially declare a president-elect.
Pena Nieto, 45, is set to return the PRI to power after 12 years in opposition. The party ruled Mexico for seven decades straight and often turned to authoritarian tactics to stifle political rivals and rig elections.
Lopez Obrador said the party resorted to its old tricks after polls showed he was gaining ground late in the campaign and a student-led movement began to rally against Pena Nieto's candidacy.
Backed by the Party of the Democratic Revolution (PRD) and a coalition of smaller left-wing parties, Lopez Obrador also claims the PRI pressured local officials to line up votes for the party in the many states where it holds power.
Ricardo Mejia, a spokesman for Lopez Obrador's legal team, said the lawyers will present proof that Pena Nieto spent 4 billion pesos ($296.51 million) during the campaign, 12 times the legal limit of 330 million pesos.
The PRI denies the accusations and has filed a legal complaint against Lopez Obrador for making false statements.
PRI chairman Pedro Joaquin Coldwell said Lopez Obrador alienated many voters with his protests in 2006 and called him a "sore loser" who was backtracking on a promise made before the vote to accept the election results.
"We will prove the falsehood of his arguments," Joaquin Coldwell told a news conference. "And demonstrate the legality of our triumph."
Pena Nieto, the former governor of the State of Mexico, was pegged to win the race by double digits in opinion polls throughout. In the end, he won by about 6.6 percentage points and the PRI failed to clinch a majority in either the Senate or the lower house of Congress.
Lopez Obrador said the polls are a clear sign of the media propping up Pena Nieto's campaign. At least one of the major pollsters has since admitted the readings were inaccurate.
Media reports pointed to the country's largest broadcaster Televisa receiving payments to promote Pena Nieto when he was governor and openly opposing Lopez Obrador's first presidential bid. Both the PRI and Televisa deny the claims.
Calderon's National Action Party (PAN), whose candidate Josefina Vazquez Mota finished third, voiced concerns about vote buying and media manipulation but said it would not join forces with Lopez Obrador in his push to annul the results.