The impeachment process against Brazilian President Dilma Rousseff has been thrown into doubt.
The acting speaker of Brazil’s lower house, Waldir Maranhao, has annulled a vote in the lower house on 17 April that allowed the proceedings to go on to the Senate.
The Senate was scheduled to vote on whether to start an impeachment trial on Wednesday.
It is not currently clear if that vote will now happen.
Mr Maranhao said there had been irregularities during the lower house session in which its members overwhelmingly voted in favour of the impeachment process going ahead.
He said members of the lower house should not have publicly announced what their position was prior to the vote, and that it had been wrong of party leaders to instruct their members how to vote.
Mr Maranhao called for a new vote in the lower house, but it is not yet clear whether the senate will agree to return the proceedings to the lower house.
It is also not known whether Mr Maranhao’s decision can be overruled.
Mr Maranhao, who opposed the impeachment process in the 17 April vote, only took over as the speaker of the lower house last week, after the previous speaker, Eduardo Cunha, was suspended.
Mr Cunha, an outspoken critic of President Rousseff, led the impeachment drive against her.
Reacting to the news, Ms Rousseff urged “caution”, adding that there was a “hard fight ahead”.
Ms Rousseff has said the efforts to impeach her amount to “a coup attempt”.
She has accused Mr Cunha and Vice-President Michel Temer of being the “ringleaders of the coup”.
Mr Temer would step in as interim president if Ms Rousseff were to be suspended from office.
In a BBC interview last week, Ms Rousseff said she was an “innocent victim” and that she would fight on.
She is accused of manipulating the government budget ahead of her re-election in 2014. The president has defended her fiscal measures as common practice in Brazil.
Following Mr Maranhao’s decision, Brazil’s currency, the real, lost more than 4% against the dollar, while the country’s stock exchange slipped more than 3%.
Investors have criticised Ms Rousseff and her Workers’ Party for what they say are interventionist policies and see Mr Temer as being more market-friendly.
Brazil is in its worst recession in 25 years, with inflation at a 12-year-high in 2015.
The president’s approval ratings have plummeted recently, and recent polls suggest most Brazilians support her removal from office.