The impeachment process against President Dilma Rousseff was thrown into disarray Monday after the leader of Brazil’s lower house moved to annul its vote last month to put her on trial.

The announcement was an unexpected reprieve for Rousseff, coming just two days ahead of a second impeachment vote, this one in Brazil’s Senate. But the relief was likely to be short-lived.

By the late afternoon, the president of Brazil’s Senate said the upper chamber vote would go forward as planned, injecting yet another dose of uncertainty into the country’s political crisis. The standoff could end up at Brazil’s Supreme Court.

The day’s confusion started with the publication of a statement by Waldir Maranhão, a little-known congressman who was named interim speaker of Brazil’s Chamber of Deputies just last week. Maranhão said he had accepted a request by Attorney General José Cardozo, who is defending Rousseff, to annul the April 17 impeachment vote in the lower house, citing procedural irregularities.

Maranhão said lawmakers should not have announced their votes in advance and should not have been told how to vote by party leaders. He also said that Rousseff’s defense should have been last to speak before voting began.

“For these reasons I annulled the session . . . and decided that a new session should take place,” Maranhão said. He did not set a date. About 70 percent of Brazilian deputies voted against Rousseff in last month’s session, so dozens of lawmakers would have to change their minds about her impeachment for a future vote to break her way.

Still, the annulment announcement touched off a scramble in Brazil’s National Congress, as Rousseff’s opponents reacted with angry disbelief and began questioning Maranhão’s authority to cancel a vote that had taken place.

Even Rousseff seemed to be whipsawed by the move.

“I don’t know the consequences,” she said in a speech, cautioning a crowd of cheering supporters to temper their enthusiasm. “We have to find out what’s happening.”

Maranhão is a member of the Progressive Party, a centrist block that was part of Rousseff’s governing coalition until recently and whose deputies then voted for her impeachment.

Rousseff’s supporters said Maranhão’s move reflected public disapproval of the way the April 17 vote unfolded, with lawmakers taunting, shoving and even spitting on one another in a raucous session carried live on national television.

“The country is shocked at what happened in the chamber,” José Guimarães, the leader of Rousseff’s Workers’ Party in the lower house, told TV Globo.

Maranhão became acting speaker of the house last week after Eduardo Cunha, the elected speaker, was suspended by Brazil’s Supreme Court. Cunha is accused of corruption by the same court.

Rousseff faces impeachment on charges that she used improper loans from government banks to fund popular social programs. Senators must decide whether this amounts to what is considered a “crime of responsibility.” Rousseff’s opponents said she deceived Congress and the Brazilian public by concealing budget gaps brought on by her poor management of the economy.

Rousseff insists that she did nothing wrong and that the budgetary tactics have been a standard practice of Brazilian presidents.

Renan Calheiros, the president of the Senate, said Wednesday’s impeachment vote would go ahead as planned.

“To accept this game-playing with our democracy would make me personally responsible for a delay in the process,” Calheiros told the Senate. “An autocratic decision cannot override the will of the legislature.”

Under the usual procedure, if 41 of Brazil’s 81 senators vote to impeach Rousseff, she would be put on trial and forced to step down temporarily pending a final vote. It wasn’t clear if Maranhão’s attempt to annul the lower house vote could stop that.

“What will happen on Wednesday is they may get more votes against Rousseff than they had originally thought,” said David Fleischer, an emeritus professor of political science at the University of Brasilia. “That’s called a backfire.”

Joaquim Falcão, a professor of constitutional law at the Getulio Vargas Foundation law school in Rio, said that because Maranhão’s decision lacks “legal authority,” it would not be able to stop the impeachment process against Rousseff.

Ricardo Ismael, a professor of political science at the Pontifical Catholic University of Rio de Janeiro, said the matter would probably go to the Supreme Court. He predicted that the court would overturn the nullification and put the impeachment process back on track.

The annulment attempt managed to stir up more chaos in Brazil, rattling financial markets and causing a slide in the value of the Brazilian currency. With the Rio Olympic Games less than three months away, the nation of 200 million is in the grips of its worst economic crisis since the 1930s. Investors have reacted negatively to signs of more turmoil ahead.

“We are in a bad position,” Ismael said. “This is going to increase political instability.”