The Greek PM has warned the nation of a collapse in living standards if MPs fail to pass an unpopular austerity bill demanded in return for a 130bn-euro ($170bn; �110bn) bailout.
In a TV address, Lucas Papademos said Greece was "just a breath away from Ground Zero".
The cabinet has approved the measures but five government ministers resigned.
Unions are holding a 48-hour strike, and thousands of protesters rallied in central Athens against the measures.
Riot police were on standby after clashes on Friday, but the demonstrations were mostly peaceful.
The austerity measures are being demanded by the eurozone and IMF - they must now be passed by the Greek parliament and approved by European finance ministers.
Some MPs from the governing parties are expected to vote against the bill, the BBC's Mark Lowen in Athens reports.
But analysts say the package should still have enough support in parliament, because Pasok, the largest party, and its coalition ally New Democracy account for more than 230 deputies out of a total of 300. Catastrophe fear
Mr Papademos said the measures would "decide the country's future" and enable it to stay inside the euro. Continue reading the main story What went wrong in Greece?
An old drachma note and a euro note
Greece's economic reforms, which led to it abandoning the drachma as its currency in favour of the euro in 2002, made it easier for the country to borrow money.
The opening ceremony at the Athens Olympics
Greece went on a big, debt-funded spending spree, including paying for high-profile projects such as the 2004 Athens Olympics, which went well over its budget.
A defunct restaurant for sale in central Athens
The country was hit by the downturn, which meant it had to spend more on benefits and received less in taxes. There were also doubts about the accuracy of its economic statistics.