Participants in yesterday's rally in Sao Paulo claim Rousseff knew of a scheme that siphoned money from the state-owned oil company Petrobras and funneled it to the governing Workers' Party.
A convicted money launderer has told investigators that the Workers' Party benefited from the scheme and that Rousseff had direct knowledge of it, though he has so far offered no proof. The president has strongly denied the accusations.
Rousseff was re-elected last Sunday with 51.6 percent of the votes against 48.4 per cent for centre-right challenger Aecio Neves.