Brazilian President Dilma Rousseff's chances of surviving impeachment appeared diminished on Wednesday, a day after two parties decamped from her governing coalition, complicating her bid to defeat the process in a crucial vote expected this weekend.

Local news reports said the pullouts have sparked growing despondency among members of Rousseff' left-leaning Workers' Party ahead of the vote expected Sunday in the Chamber of Deputies. That vote will determine whether to move ahead with the impeachment process against Rousseff, based on allegations her administration violated fiscal rules.

The pro-impeachment camp needs two-thirds of the 513 votes in the lower house, or 342 votes, in order to send the proceedings to the Senate.

While the results remain too close to call, Tuesday's pullout of the majority of the deputies for the Progressive Party, which holds 47 seats in the lower house, as well as the Party for a Renovated Brazil, which holds 22 seats, made it that much harder for Rousseff to defeat the vote. According to a tally in the Folha de S. Paulo, 281 legislators have come out for impeachment, while 113 are opposed and 119 are undecided.

The Social Democratic Party's members in the lower house were meeting to decide whether to support the impeachment. The party holds 36 seats in the Chamber of Deputies.

"Ministers close to Dilma believe the battle against impeachment is virtually lost," Monica Bergamo, a respected political columnist with the newspaper, wrote on Wednesday. "Not all of them have definitively thrown in the towel, but the consensus is that the government is going through its worst moment."

News reports have also said Eduardo Cunha, the speaker of the lower house and driving force behind the impeachment, is planning to organize Sunday's vote in the least favorable way possible for the president. O Globo newspaper reported that Cunha wants to start the voting with representatives from the southern states, which tend to be strongly anti-Rousseff, and work up to the largely pro-government states at the end, in order to create a wave of support for impeachment. An official announcement on order of the vote is expected later Wednesday, the report said.

Rousseff has seen her approval ratings tumble amid the worst recession in decades, a spike in both joblessness and inflation, and a spiraling corruption investigation at the state-run Petrobras oil company that has ensnared dozens of top politicians across the political spectrum, as well as some of Brazil's richest and most powerful business executives.

The impeachment proceedings against her stem from allegations her administration violated fiscal rules to mask budget problems by shifting around government accounts. Opposition parties claim sleight-of-hand accounting moves allowed her to boost public support and say impeachment is in line with the wishes of the majority of Brazilians.

Rousseff and her supporters say the allegations are bogus and insist financial maneuvers like the ones she made are common practice, used by two prior presidents. She has repeatedly denounced the proceedings as an attempted coup and a blatant power grab by her foes.

If the pro-impeachment camp wins Sunday's vote, the proceedings move to the Senate, where a vote will determine whether to begin a trial against Rousseff. If that happens, she would immediately be suspended from office and Vice President Michel Temer would take over.