Brazilian President Dilma Rousseff has vowed to fight to "the last minute" despite the desertion of two allies ahead of Sunday's impeachment vote.
Ms Rousseff, who says her opponents are plotting a "coup", faces claims she manipulated government accounts.
On Tuesday two parties formerly in her coalition said they would vote in favour of the impeachment motion.
If two-thirds of the lower house vote for impeachment, the motion will then pass to the Senate.
The Progressive Party (PP), which quit the coalition on Tuesday, says most of its 47 MPs would vote for the impeachment, and the Republican Party (PRB) said its 22 members had been told to vote for it.
The move comes weeks after the PMDB, the largest party in the the lower house, voted to leave the coalition.
MPs from Ms Rousseff's own Workers' Party are said to be increasingly despondent about Sunday's vote.
The allegations, which Ms Rousseff denies, are that she juggled the accounts to make her government's economic performance appear better than it was ahead of her election campaign two years ago.
The president's supporters say the issue is not valid grounds for impeachment anyway.
While Tuesday's developments have weakened Ms Rousseff's position ahead of the impeachment vote, its outcome is uncertain, with many members of the lower house still undecided.
In an interview on Wednesday the president said she would fight the impeachment proceedings "until the last minute of the second half", employing a metaphor from the world of football.
On Tuesday Ms Rousseff seemed to suggest that her Vice-President, Michel Temer, was one of the ringleaders of the "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".
On Monday evening, amid rowdy scenes, a 65-member congressional committee voted 38 to 27 to recommend going ahead with impeachment proceedings.
MPs are due to start debating on Friday, officials said, with voting beginning on Sunday at about 14:00 (17:00 GMT). The result should be known later in the evening.
Security is expected to be stepped up around the Congress building in Brasilia as the vote takes place.
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 Mr Cunha.
However, he is facing money-laundering and other charges.
Where did it go wrong? Daniel Gallas, Sao Paulo
From billions being stolen from state oil giant Petrobras by private construction firms and politicians, to a powerful senator negotiating for a key witness to flee from jail, the country has been rife with jaw-dropping corruption revelations.
Yet with all the investigations, one person has managed to keep a fairly clean record - President Dilma Rousseff.
Ms Rousseff's personal record on corruption may be untarnished so far - but her handling of the economy has been highly controversial. And this is the argument the opposition has been advancing to get her impeached.
Making what critics say are bad decisions on the economy is not a crime. But one of the measures taken by Ms Rousseff and her team back in 2014 was deemed illegal by a federal court.
Brazilian governments are required to meet budget surplus targets set in Congress. Ms Rousseff is accused of allowing creative accounting techniques involving loans from public banks to the treasury that artificially enhanced the budget surplus.
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.