Brazil's Supreme Court on Wednesday rejected an appeal by President Dilma Rousseff to block a Senate vote on her impeachment.
The decision by Judge Teori Zavascki leaves the way clear for the Seante to decide whether to suspend Rousseff and put her on trial over allegations she illegally manipulated the budget to hide a growing fiscal deficit.
Senators began debating Wednesday ahead of a vote expected to last well into the night.
If the Senate votes by a simple majority to consider the impeachment, Rousseff will be suspended for 180 days, during which time the Senate would investigate the case.
A two-thirds majority would then be required in the upper house to permanently remove her from office.
In a last-ditch effort to block the vote, Rousseff had filed an appeal late Tuesday asking the court to suspend the Congressional proceedings because it constituted an "abuse of power."
The legal tactic was the latest in a series of dramatic manoeuvres around the process to remove Rousseff from office.
In April, the lower house of parliament voted to impeach Rousseff, who has been president since 2011 and is the first woman to hold the office.
But on Monday, Waldir Maranhao, the interim head of the legislature's lower house, the Chamber of Deputies, threw the impeachment effort into disarray by annulling that vote, citing procedural problems.
He then reversed the decision several hours later, setting the stage for the vote in the Senate.
In her filing to the Supreme Court, Rousseff accused bitter rival and former speaker of the Chamber of Deputies, Eduardo Cunha, of abusing his power in calling the April vote. Cunha was suspended last week over accusations of obstructing a corruption investigation against him.
Deeply unpopular, Rousseff's presidency has been battered by high-profile corruption scandals, political paralysis and a sharp economic downturn. Some 11 million people are out of work.
Rousseff faces impeachment over accusations of tampering with figures to disguise the size of Brazil's budget deficit during her 2014 re-election campaign. She has denied any wrongdoing, and cast the efforts to oust her as a coup.