Taiwan's High Court will today hear an application to nullify the country's recent election result in which the incumbent President Chen Shui-bian was the narrow winner.
The ruling sought by the main opposition, which lost last month's poll, could lead to a speedy recount and help resolve the political crisis that has developed.
The closely fought March 20th election has divided the island and triggered alarm in China, which views pro-independence policy of Mr Chen as a threat to regional stability.
Mr Chen defeated his Nationalist Party challenger, Mr Lien Chan, by just 30,000 votes out of more than 13 million cast. Mr Lien says a mysterious election-eve shooting that slightly wounded the president caused a swelling of sympathy votes.
Mr Lien's legal action aims to nullify Mr Chen's victory and cites voting irregularities and a record 330,000 invalid ballots that were triple the number rejected in the last presidential election four years ago.
The court will decide whether to re-examine the invalid ballots. Mr Chen has agreed to a full judicial recount.
Mr Lien has also demanded an independent inquiry into the assassination attempt and has suggested it could have been staged.
Mr Lin Fong-cheng, secretary-general of the Nationalist Party, warned of "endless" protests for the next four years if an impartial investigation was not held into the shooting.
Half a million people led by Mr Lien besieged the presidential palace on Saturday to dispute the election outcome in the island's biggest political protest. Another rally of up to 50,000 is scheduled for tomorrow.