According to the demonstrators there were at least 500 vote rigging reports, including vote buying.
Mexico leftists from the camp of Andres Manuel Lopez Obrador, a presidential candidate of the Democratic Revolution Party, have been voicing criticism of the campaign where biased media allegedly favored Pena Nieto of the Institutional Revolutionary Party, particularly Mexico's semi-monopolized television industry.
Lopez Obrador was predicted to lose to Pena Nieto by a double-digit margin. But with 99 percent of the vote tallied in the preliminary count, Lopez Obrador of the Democratic Revolution Party trails by just 6% behind the election's apparent victor.
Pollsters claimed that some voters changed their minds and switched to Lopez Obrador in the final week before Sunday's election, an argument which didn’t convince the left, who argued from the start of the campaign that pollsters were manipulating pre-election surveys to favor Pena Nieto as a way to boost the idea that the PRI candidate was far out in front.
Lopez Obrador said he would not accept the preliminary election results reported by the Federal Elections Institute and would wait until Wednesday, when the official results are to be announced, before deciding what he will do. Mr. Obrador said he probably would challenge Sunday's vote results. "We will not accept a fraudulent result," he said.