Brazil’s largest party, the Brazilian Democratic Movement Party (PMDB), has voted to pull out from the governing coalition.
The centrist party called for an “immediate exit” from President Dilma Rousseff’s government.
The move could hasten impeachment proceedings against President Dilma Rousseff, correspondents say.
Opposition lawmakers want to remove Dilma Rousseff over claims that she manipulated accounts to hide a growing deficit.
The PMDB’s decision comes a day after tourism minister Henrique Eduardo Alves from the party stood down.
At a leadership meeting on March 29, the PMDB decided that its six remaining ministers in Dilma Rousseff’s cabinet must resign or face ethics proceedings.
“The decision was taken by acclaim in a historical meeting marking the withdrawal from Dilma [Rousseff’s] government,” Senator Romero Juca tweeted.
Dilma Rousseff could now be temporarily suspended from office by Congress as early as May.
She would be replaced by Vice President Michel Temer, leader of the PMDB, while the Senate decides if she should permanently leave her post.
Analysts say a considerable number of lawmakers from the PMDB have felt uneasy about their alliance with the left-wing Workers’ Party for a while.
Their unease has been compounded by calls for Dilma Rousseff’s impeachment and a widening corruption scandal involving senior members in the Workers’ Party.
Dilma Rousseff needs one third of the members of the lower house of Congress to vote against her impeachment for the proceedings to be shelved.
Without the PMDB, the president could lose as many as 69 votes at once in the 513-member Chamber of Deputies.
Another of Dilma Rousseff’s coalition partners, the center-left Social Democratic Party (PSD) said it had given its lawmakers a free vote in any possible impeachment proceedings.
On March 28, Dilma Rousseff’s mentor and predecessor in office, Luiz Inacio Lula da Silva, likened the moves to impeach her to a coup.
However, Luiz Inacio Lula da Silva himself is under pressure.
The Supreme Court suspended Luiz Inacio Lula da Silva’s appointment as Dilma Rousseff’s chief of staff earlier this month and is due to take a final decision on the matter next week.
Opponents of the government said Dilma Rousseff had given Luiz Inacio Lula da Silva the post so he could escape investigation and possible proceedings over allegations of money laundering.
Under Brazilian law, cabinet members can only be investigated by the Supreme Court, not by lower courts.
There have been mass protests demanding the impeachment of Dilma Rousseff in cities like Sao Paulo and Rio de Janeiro.
There have also been rallies in support of the government by those who say Dilma Rousseff is the victim of a campaign to drive the Workers’ Party from government.