The interim head of Brazil's House of Deputies said Monday that he has overturned last month's vote by the lower chamber to impeach President Dilma Rousseff, citing procedural mistakes.
Waldir Maranhao said he had annulled the April 18 vote and called for a new vote.
His decision could face a legal challenge.
The full Senate had been expected to vote Wednesday to decide whether Rousseff should be subjected to a trial in the upper chamber on allegations that she illicitly hid a surge in Brazil's budget deficit during her 2014 re-election campaign.
It was not immediately clear if the Senate vote would still be held as scheduled.
The Senate was to decide whether Rousseff should be suspended from office for maximum of 180 days, during a detailed legal examination of the charges against her. Vice President Michel Temer would assume presidential duties during her suspension, including opening the Olympics in August.
Rousseff and her supporters have called the impeachment vote an attempted coup, and have pointed out she has not been charged with any crime.
Rousseff's presidency has been battered by a recession brought on by a drop in commodities markets and slowing global economy. Unemployment in Brazil rose to 9.6 million workers in 2015.