Front-running former president Luiz Inacio Lula da Silva called on his supporters to take to the streets to help him win Brazil's election in October and deny far-right incumbent Jair Bolsonaro a second term.
The leftist leader and Workers Party (PT) founder said the Brazilian economy will recover solid growth only if there is income distribution in the South American country.
Speaking at the convention of the Brazilian Socialist Party (PSB), Lula criticised his rival for treating Brazil's armed forces as if they were his political tool.
Bolsonaro, a former Army captain who was elected to Congress three decades ago, said on Sunday that the Army was on his side in a speech at the official launch of his re-election bid.
He has tried to get the military to endorse his criticisms of Brazil's electronic voting system, raising fears he might not concede if defeated or try to encourage a coup.
Lula, who governed Brazil for two terms 2003-2010 during a period of fast growth thanks to a commodities super-boom, has said he trusts the armed forces will respect the Constitution and accept him returning to office if he wins the most polarised Brazilian election in decades.
"I never had any problems with any military commander or with any of the armed forces," the former union leader said.
Lula said Workers Party aides have told him not to campaign in the open for fear of violence, but he said he plans to attend public rallies from now on and called on his supporters to avoid provocations.
"We will win by having courage. We have to go to the streets to show that the Brazilian people really want democracy. We cannot give in to this bully," he said, referring to Bolsonaro.