Tens of thousands of people demonstrated Friday in support of embattled President Dilma Rousseff and her predecessor, Luiz Inacio Lula da Silva.
"There will be no coup," Lula shouted to his supporters in Sao Paulo.
Organizers of the demonstration said 250,000 people turned out. Other sources estimated about 95,000.
Rallies took place acrosss the country. The portal Folha S Paulo said they were held in 22 states. The rallies were called by unions and Rousseff's Workers Party, which has ruled Brazil since 2003.
Lula on Thursday denounced the public release of wiretapped phone conversations between him and Rousseff.
Lula, 70, complained in an open letter that his privacy had been damaged by the release of the information.
"I merely expect justice," Lula wrote, calling the actions of judicial authorities sad and shameful.
Lula, who was president during 2003-11, is under investigation in a far-reaching scandal involving billions of dollars in alleged kickbacks by state-owned oil company Petrobras.
A taped telephone conversation between Lula and Rousseff was released Wednesday by the judge handling the Petrobras case. Their discussion of the criminal investigation against Lula and the possibility of his appointment was interpreted by Brazilians as evidence that the long-time friends were collaborating to keep him from being prosecuted.
This week, Rousseff named Lula as her chief of staff, a move that is being viewed as a way to shield him from prosecution. A judge later vetoed Lula's appointemnt, saying it would conflict with the case against him.
Earlier this month, Brazilian police raided Lula's home and briefly took him in for questioning.
Congress late last year opened impeachment hearings against Rousseff, who is profoundly unpopular amid a severe economic downturn and political gridlock in the world's fifth largest country by population.
She is accused of misusing public money by falsifying state accounts. The cloud of suspicion hanging over her has grown because she was energy minister and chaired the Petrobras supervisory board under Lula.
In the Petrobras scandal, various firms including Brazil's largest construction companies are believed to have paid billions of dollars in bribes to obtain lucrative contracts with the oil monopoly.
Some of the allegations leveled against Lula involve his home on the Atlantic coast. He denies having received any favours from a construction company.
Police used tear gas and rubber bullets against protesters at the National Congress building in Brasilia Thursday.