The president is now dealing with a further blow to her bid to stave off impeachment.
The PP said most of its 47 lawmakers would vote for Dilma Rousseff to be impeached.
Last month the PMDB, the largest party in Brazil’s governing coalition, also voted to leave.
Dilma Rousseff, who faces an impeachment vote in the lower house on April 17, says her opponents are plotting a “coup”.
They claim she manipulated accounts to hide Brazil’s growing deficit ahead of her election campaign two years ago. Dilma Rousseff denies this and her supporters say the issue is not valid grounds for impeachment anyway.
A PP spokeswoman told AFP news agency on April 12: “The party decided to withdraw from the… alliance, by majority decision.”
The PP is the fourth-largest party in the 513-seat lower house but it is not clear how its departure from the government might affect April 17 vote.
A two-thirds majority – 342 alawmakers – is needed to send the impeachment case to the Senate.
A recent poll, before the PP’s announcement, showed 300 in favor of impeachment and 125 opposed, leaving 88 lawmakers still undecided or not stating their position.
On April 122, Dilma Rousseff suggested that Vice-President Michel Temer was one of the ringleaders of the “coup” attempt against her.
She said a widely distributed audio message of Michel Temer appearing to accept replacing her as president, was evidence of the conspiracy. However, she did not identify him by name.
“They now are conspiring openly, in the light of day, to destabilize a legitimately elected president,” Dilma Rousseff said.
She referred to “the chief and… the vice-chief” of the plot, an apparent reference to Michel Temer and lower house speaker Eduardo Cunha.
Brazil is “living in strange times”, she said, “times of a coup, of farce and betrayal”.
Michel Temer has said that the message was released by accident.
Speaking in an interview with the conservative Estado de Sao Paulo newspaper on April 12, Michel Temer argued that he had spent weeks away from the capital Brasilia specifically so that no-one could accuse him of plotting behind the scenes.
On Monday evening, amid rowdy scenes, a 65-member congressional committee voted 38 to 27 to recommend going ahead with impeachment proceedings.
Lawmakers are due to start debating on April 15, officials said, with voting beginning on April 17 at about 14:00. 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 Dilma Rousseff’s opponents say the impeachment is supported by most Brazilians, the president’s supporters have labeled it a flagrant power grab by her political enemies.
If Dilma Rousseff and Michel Temer are both suspended from office, the next in line to assume the presidency is Eduardo Cunha.
However, Eduardo Cunha is facing money-laundering and other charges.
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