By Chris Hogg
BBC Taiwan correspondent
Taiwan's High Court is due to rule on whether President Chen Shui-bian's election in March should be overturned because of alleged fraud.
President Chen was shot on the eve of voting
The lawsuit brought by the opposition nationalists accuses the president of irregularities, including staging his own shooting on the eve of the poll.
This is the first of two legal challenges aimed at unseating the president.
Taiwan's government has asked people not to protest after the result.
This lawsuit is directed at President Chen himself. It claims he acted illegally, holding a referendum on security issues at the same time as the presidential poll.
It accuses him of staging his own shooting on the eve of election day, and of taking advantage of the attack by putting the security forces on alert.
The opposition nationalist Kuomintang party (KMT) claims that many soldiers and policemen - their traditional supporters - were unable to vote as a result of their emergency duties. President Chen was elected with a majority of fewer than 30,000 votes, less than 0.5% of the ballots cast.
The president denies the allegations, and his supporters are confident he will be vindicated by the court.
But Thursday's decision will not be the end of the story. Whatever the High Court decides, the loser can appeal to Taiwan's Supreme Court, a process that could take up to six months to complete.
There is also a second legal challenge under way, this time aimed at the Central Election Commission.
The opposition is asking the courts to overturn the election because of the commission's failure to suspend the vote in the wake of the shooting.
Fears that these court cases could stir up emotions just over five weeks before parliamentary elections in Taiwan have led to appeals by the government for calm, whatever the verdict announced by the High Court.