Brazil's lower house of parliament has begun a debate ahead of a vote on Sunday on the impeachment of President Dilma Rousseff.
Opposition MPs chanted "Dilma Out" as the session got under way.
Brazil's Supreme Court rejected a government injunction against the vote.
Ms Rousseff is accused of manipulating government accounts ahead of her re-election in 2014. She denies the charges and accuses opponents of plotting a "coup".
Her supporters say the issue is not valid grounds for impeachment.
Ms Rousseff has vowed to fight to "the last minute" despite the desertion of three allied parties ahead of Sunday's vote, which begins at about 14:00 (17:00 GMT).
Brazilian media predict a close vote, with two polls putting the number of those in favour of impeachment at 342 - the crucial two-thirds needed to send the motion to the upper house, the Senate.
If the Senate endorses the move, Ms Rousseff will be suspended for up to 180 days whilst an impeachment trial is held.
Brazilian Attorney-General Jose Eduardo Cardozo took the floor to warn against voting to impeach the president, calling the process a "violent act with no parallel against democracy".
"History will never forgive those who broke with democracy," Mr Cardozo said.
But one of the MPs spearheading the petition to dismiss the president, Miguel Reale Junior, said Ms Rousseff deserved to go because "she was extremely irresponsible and knocked out the country".
He said the president's actions had led to Brazil's difficult economic situation.
"Are you going to tell me that isn't a crime?", he added.
The Supreme Court made its decision in an extraordinary session, with seven of 10 justices voting to reject the motion even before the Supreme Court session had finished.
On Tuesday, Ms Rousseff seemed to suggest that her Vice-President, Michel Temer, was one of the ringleaders of a "coup" attempt against her.
She said a widely distributed audio message of Mr Temer appearing to accept replacing her as president was evidence of the conspiracy. However, she did not identify him by name.
Brazil is "living in strange times", she said, "times of a coup, of farce and betrayal".
While President Rousseff's opponents say the impeachment is supported by most Brazilians, the president's supporters have labelled it a flagrant power grab by her political enemies.
If the president and Mr Temer were both suspended from office, the next in line to assume the presidency would be lower house speaker Eduardo Cunha.
However, he is facing money-laundering and other charges.
What happens next?
Lower house vote: An impeachment vote is expected in the lower house on Sunday. A two-thirds majority is required for it to go forward to the Senate.
Senate vote on trial: If Ms Rousseff case is sent to the Senate, a simple majority is enough to suspend her for up to 180 days while she is put on trial. Vice-President Michel Temer would step in during this period.
Impeachment vote: For Ms Rousseff to be removed from office permanently, two-thirds of the Senate would have to vote in favour. Mr Temer would remain president for an interim period should this happen.