The Israeli Prime Minister Mr Ariel Sharon issued a last-minute appeal to voters in his Likud Party to support his plan to withdraw from the Gaza Strip, saying that rejection in a party referendum today would threaten the country's future.
Today's Likud vote was a critical test for Mr Sharon. A loss would likely spark a major political crisis, including a possible Cabinet reshuffle, a split in the hard-line party or even early elections.
Mr Sharon remains determined to carry out the withdrawal, regardless of the outcome of the vote, people close to him said.
Other officials hinted that Mr Sharon might seek a nationwide referendum on his plan - a vote he would be likely to win.
In an encouraging sign for Mr Sharon, a poll released today indicated the Likud race was too close to predict. Most recent polls have pointed to a loss.
"The vote is important since it will decide if Israel will move forward in all realms - security, the economy, education and employment, relations with the United States - or will fall backward," Mr Sharon told his Cabinet today.
"Everyone has to think about the future of its children and vote for my plan."
Mr Sharon has proposed withdrawing from the Gaza Strip, including the evacuation of some 7,500 settlers, taking down four small West Bank settlements and completing construction of a West Bank separation barrier by the end of 2005.
Mr Sharon argues that this would give Israel defensible borders and reduce friction with the Palestinians in the absence of a final peace deal.
Opponents say an Israeli withdrawal will be seen as victory by Palestinian militants, and that Sharon is betraying the settlers. For decades, Sharon was the foremost champion of settlement expansion.
The opponents have run a tight campaign, plastering Israeli streets with posters and visiting thousands of Likud members in their homes. At a main polling station in Jerusalem Sunday, opponents holding banners and flags greeted voters as they arrived. No supporters of the plan were visible.
"We won't stop until the very end doing everything that we can," Likud Cabinet minister Mr Uzi Landau, who has led the opposition, said on Army Radio.