Investigators are examining allegations of vote-buying by the island's main opposition Nationalist Party, a prosecutor and local media said today.
The investigation comes two days before Taiwan's general election.
The Nationalists, the world's richest political party with assets of $2.4 billion, came under investigation after a disgruntled party member tipped off anti-corruption officials about alleged vote-buying, the sources said.
The Nationalist Party denies any wrongdoing.
Investigators of the high court prosecutor's office, the Anti Black Gold Centre, said in a statement they have traced several cheques to a political party that were deposited into the bank account of a campaign aide accused of buying votes.
The government has intensified a crackdown on vote-buying, which has led to the indictment of 89 people. Defendants included three incumbent legislators seeking re-election from both the ruling and opposition parties.
The once-formidable Nationalists are expected to lose their parliamentary majority in elections on Saturday in a deepening crisis after their 55-year monopoly on power ended in last year's presidential election defeat.
No party is expected to emerge with a parliamentary majority. Political horse-trading is likely to follow, with President Mr Chen Shui-bian, whose 17 months in office have been marred by gaffes and policy flip-flops, seeking allies to form a coalition.