Brazil’s President Dilma Rousseff has asked the Supreme Court to block impeachment proceedings against her – in a final attempt to stop the process hours before a crucial Senate vote.
Ms Rousseff’s lawyers alleged bias and irregularities. Similar attempts have been rejected by the court.
Ms Rousseff could be suspended for up to 180 days if the senators vote for a full trial on Wednesday.
Earlier, her supporters set up burning barricades and blocked roads.
The roadblocks caused widespread disruption across all Brazilian states.
Waldir Maranhao, acting speaker of the lower house of Congress, caused fresh surprise on Tuesday when, less than 24 hours after suspending a vote in the chamber that had allowed the impeachment process to go ahead, he reversed his decision.
Previously he had argued that the 17 April vote had breached Congress rules. Members had voted overwhelmingly in favour of the impeachment process going ahead.
The president is accused of illegally manipulating finances to hide a growing public deficit ahead of her re-election in 2014, which she denies.
A critical moment: analysis by Wyre Davies, BBC Brazil correspondent
What has been a long, damaging and divisive political process is at a critical moment as the 81 members of the Brazilian Senate prepare to vote on whether or not to subject Dilma Rousseff to a full impeachment trial.
The beleaguered president denies the charges against her – that she illegally concealed the scale of the budget deficit. Brazil’s first female leader says that what is really happening, first in the lower house of Congress and now in the Senate, is a judicial coup by her political opponents to remove her from office.
Whatever the real reasons for impeachment, there is no doubt that Ms Rousseff’s leftist Workers’ Party is deeply unpopular, with Brazil in the middle of an economic crisis and her government embroiled in a huge corruption scandal.
In a recent interview with the BBC, Dilma Rousseff appeared to acknowledge that she would be suspended pending an impeachment trial but she said would fight to clear her name and fully intended to resume the final two years of her presidency.
‘I will not resign’
Brazil’s Attorney General Eduardo Cardozo, the government’s top lawyer, said on Tuesday that the Supreme Court should annul impeachment proceedings, arguing that they were politically motivated.
The court is already considering the appeal, but it is not known when a ruling will be issued.
Meanwhile, Ms Rousseff promised to fight to the end.
“I will not resign, that never crossed my mind,” she said during a speech at a women’s rights conference in the capital Brasilia on Tuesday.
Is Ms Rousseff loses the Senate vote, she will be replaced by Vice-President Michel Temer while the trial lasts.
She says Mr Temer is a traitor who is taking part in a political coup against her democratically elected government.