Thousands of people took to the streets across Brazil demanding the resignation of President Michel Temer, who is the target of a corruption investigation.
Organised mainly via social media, the largest protests on Thursday took place in Sao Paulo, Rio de Janeiro, and the nation's capital, Brasilia, Efe news reported.
Besides Temer's departure, demonstrators also called for early general elections.
The protests materialised hours after Brazil's Supreme Court authorised an investigation into allegations Temer encouraged the payment of bribes to a former top lawmaker convicted earlier this year of graft.
Justice Edson Fachin, who is overseeing cases related to the investigation of a $2 billion corruption scheme centred on state oil company Petrobras, approved the probe of the president's conduct.
Temer's legal troubles are the latest development in the Petrobras investigation, which is known as Lava Jato (Car Wash). A former president, Luiz Inacio Lula da Silva, faces several corruption trials related to the probe.
Temer on Thursday vehemently rejected calls for him to resign from both the opposition and members of his own ruling coalition.
"I won't resign. I repeat. I won't resign, and I demand that everything be fully cleared up," the head of state said in a message to the nation from the Planalto presidential palace.
But groups of lawmakers in both chambers have already drafted bills to hold the presidential election this year instead of 2018, as scheduled.
This latest political crisis caused stock prices to plunge - and trading to be temporarily halted at the Sao Paulo Stock Exchange.
The exchange's benchmark Ibovespa index ended the day down 8.8 per cent, while the value of the Brazilian real against the dollar plunged by nearly 9 per cent.