Mexican presidential candidate Andres Manuel Lopez Obrador has called on supporters to march on the electoral tribunal to demand a full vote recount.
No let up in the campaign, Mr Lopez Obrador told supporters.
Mr Lopez Obrador rejected the tribunal's decision to recount votes from only 9% of polling stations.
"We don't want a portion of democracy. We want 100% democracy," he told thousands of supporters in Mexico City.
Official results from the 2 July vote gave victory to the conservative Felipe Calderon by half of a percentage point.
For the past week his supporters have been camped out in central Mexico City as part of a campaign of "civil disobedience" to demand a full "vote-by-vote" recount.
'Not in vain'
Mr Lopez Obrador told tens of thousands of supporters in the city's vast Zocalo Square on Sunday: "This week we are going to carry out actions of resistance."
The fight, he added, would "possibly will take more time, but will not be in vain".
Protesters blocked access to the stock exchange last week
Mr Lopez Obrador urged followers to march on the electoral tribunal headquarters on Monday, and to keep up their sit-in of the Zocalo Square and main Reforma Avenue.
The sit-ins have snarled up much of the centre of the city for the last week.
Results from the July election showed that Mr Lopez Obrador lost to Felipe Calderon by less than 0.6 of a percentage point - or about 240,000 votes out of a total electorate of 41 million.
UN and EU observers pronounced the election free and fair.
However Mr Lopez Obrador presented some 900 pages of alleged evidence of electoral irregularities to the Federal Electoral Tribunal in the hope that it would order a full recount.
But on Saturday the tribunal ruled that only the results from 11,839 polling stations - of a total of 130,500 - should be recounted, beginning on Wednesday.
The tribunal has until 6 September to make its final ruling on the winner.