TAIPEI, Taiwan (AP) _ Taiwan's main opposition party voted Wednesday to support a referendum to oust embattled President Chen Shui-bian, signaling a period of uncertainty for the island of 23 million people.

Chen, who is to complete his presidency in 2008, is facing mounting pressure over allegations that his wife and son-in-law used his position for personal gain.

The recall referendum would only be held if a two-thirds majority in Taiwan's 225-seat Legislature agrees _ an outcome that would require about 35 lawmakers from Chen's Democratic Progressive Party to side with the opposition.

That is considered extremely unlikely. Still, the opposition Nationalist Party opted to move ahead with the recall process, calculating that a prolonged public debate could further weaken the president and even force him to resign, strengthening the opposition's hand ahead of 2008 presidential elections.

It was unclear how the turmoil could affect Taiwan's tense relations with China, from which the island split amid civil war in 1949. Beijing claims sovereignty over Taiwan and has threatened force if it moves toward formal independence. China sees Chen as a radical independence supporter.

Legislative speaker Wang Jin-pyng said that Nationalist and Democratic Progressive Party legislators would meet on June 11 to try to decide on an agenda for a session to consider the recall initiative.

After Nationalist leaders approved the recall measure Wednesday, party chairman Ma Ying-jeou said it was intended to save Taiwan from Chen's excesses.

He said the opposition has urged Chen to ``take responsibility'' and resign, ``but we have found that he put the interests of the party above those of society.''

Political scientist Philip Yang of Taipei's National Taiwan University said the opposition strategy is to keep pressure on Chen in hopes of weakening support within his own party.

Before the opposition vote, Premier Su Tseng-chang, a Democratic Progressive stalwart, said the opposition was out of line.

``Chairman Ma, don't destroy the rule of law for the sake of power. Don't set a bad example,'' Su told reporters.

Last week, Chen pledged he would cede part of his powers to Su to ease pressure for his ouster. But on Monday, the opposition accused Chen of failing to honor his pledge and trying to appease public opinion by hinting he might appoint an opposition premier.

The corruption allegations center on Chen's son-in-law, Chao Chien-min, who was detained last month on suspicion of insider trading, a charge he denied.

The opposition has also accused first lady Wu Shu-chen of involvement in illicit business deals and soliciting favors from business people.

The president's office denies the charges, while Vice President Annette Lu has called the fallout Taiwan's worst political crisis in more than 25 years.

In an apparent effort to assess the situation, the U.S.-based chairman of the American Institute in Taiwan _ the de facto U.S. embassy _ arrived Wednesday.

Raymond Burghardt, a retired U.S. diplomat, has close ties to Chen and played a key role in quieting U.S. fears that Chen would raise tensions with Beijing after his election in 2000.

The president's office said Burghardt would meet Chen on Thursday.