Mr Chen's personal popularity is at an all-time low

The Nationalist party's decision means Mr Chen faces a potentially damaging grilling and vote in the Legislature.

If two-thirds of legislators vote against him, a final decision would be put to the island's electorate.

Mr Chen's DPP party holds about 100 seats in the 225-seat Legislature, suggesting he would survive the vote.

Correspondents say that the opposition wants the vote to keep pressure on Mr Chen, and strengthen its position ahead of 2008 presidential elections.

Mr Chen, who was re-elected in 2004, has seen his popularity damaged by a series of alleged scandals involving advisers and relatives, most recently when his son-in-law was detained in connection with allegations of insider trading.

Responding to the criticism, Mr Chen last week said he would hand over some day-to-day powers to his prime minister, although the opposition dismissed the concession as insufficient.

'Lame duck'

Mr Chen has also seen a slump in his personal popularity, and unease within his party following the DPP's heavy defeat in recent local elections.

With two years to go before he must step down as president, critics say that giving up his day-to-day powers risks leaving him a lame duck.

But others say that he has kept control over the most important portfolio, Taiwan's troubled relations with China. Mr Chen has infuriated China, which accuses him of wanting the island's independence.

China sees Taiwan as part of its territory and has threatened to use force if it ever moved to declare formal independence.

Mr Chen's son-in-law, Chao Chien-ming, was detained in May amid allegations he used insider information when buying shares in a property company.

Mr Chao denied the allegations.