Athens: Greek Prime Minister George Papandreou's political future hung by a thread on Thursday on the eve of a crucial confidence vote as his allies revolted against his plan for a referendum on the euro.

Papandreou called an emergency meeting of his Cabinet and socialist party lawmakers with the government now set to lose its parliamentary majority for tomorrow's vote, further adding to the turmoil in the debt-laden nation.

Finance Minister Evangelos Venizelos - a former challenger for the Pasok party leadership -- was among those who spoke out strongly against the referendum, warning it could scupper a hard-won EU debt rescue deal.

"Greece's place in the euro is a historical conquest by the Greek people that cannot be placed in question... this cannot be made dependent on a referendum," Venizelos said after returning from G20 talks in Cannes.

Other senior socialist figures also lined up to demand a unity government to pull Greece out of the economic and political mire.

"The only realistic proposal to keep the country from collapsing is to form a government of national unity," said Vasso Papandreou, head of Parliament's economic affairs committee, no relation to the Prime Minister.

The Premier, facing mounting social opposition to his austerity policies, this week called for a referendum and a confidence vote to allow him to stay the course without having to resort to early elections as demanded by the opposition.

But the gambit ran into fierce opposition both at home and abroad and sent global financial markets tumbling.  Papandreou was summoned to Cannes on Wednesday by furious eurozone leaders concerned that the 100-billion-euro EU deal hammered out on Greece's debt last week would be fatally undermined by the referendum.

European leaders warned that if Greece does not respect the terms of the rescue deal, it will not get "one more cent" from the next planned installment of EU and IMF bail-out funds.

Papandreou said the referendum could be held on December 4.

"This is a question of whether we want to remain in the eurozone. That's very clear," he told reporters.

In Athens, two socialist deputies threatened to withhold support for the government over the referendum, which would give Pasok 150 votes in the 300-seat chamber.

However, the government could still win Friday's vote, depending on the number of MPs who take part.

"I will not consent to holding a referendum. I will not give a vote of confidence to a course of destruction for my country," said one of the lawmakers, Elena Panaritis.

Development Minister Michalis Chrysohoidis insisted that ratifying the EU deal - designed to slash Greece's huge debt by nearly a third - was more important, as several junior ministers also voiced their opposition.

"The Greek people must ratify the (EU) agreement...," Deputy Finance Minister Pantelis Oikonomou said. "A referendum on other issues is wrong, it's completely untimely."

Despite the uncertainty, the Athens stock exchange was trading higher, up by 2.1 percent at midday.

In Cannes, German Chancellor Angela Merkel and French President Nicolas Sarkozy said on Wednesday they hoped Greece would stay on board, but warned that Athens would not get a free ride.

"The Greeks have to decide whether to continue the adventure with us or not," warned Sarkozy. "We hope to continue with the Greeks, but there are rules that have to be respected."

"The Europeans and the IMF can't release the sixth tranche of loans to Greece until Greece endorses the package of October 27," Sarkozy said, calling for the referendum "if one is needed" to be carried out swiftly.

Eurozone Chairman Jean-Claude Juncker said the currency union hoped to keep Greece as a member "but not at any price".

IMF chief Christine Lagarde also warned she would not move on the next tranche of the Fund's loan to Greece until "all uncertainty is removed."

The European leaders pledged to stand by the euro, even if the Greeks were to vote against it.

"If the Greeks say they do not want to stay in the euro, we will accept it, but we will not abandon the euro," Merkel said.