Socrates has vowed to resign if he fails to garner support in parliament for the fourth austerity package in a year, which aims to avert the need for a multibillion financial bailout like the ones granted to fellow eurozone members Greece and Ireland last year.

The austerity plan calls for new budget cuts, a longer freeze on retirement, new taxes, a rise in public transport fares and cuts in social programmes.

The cost-cutting plan itself will not be put to a vote. Instead opposition parties will vote at around 7:00 pm (1900 GMT), after a three-hour debate, on resolutions denouncing the plan.

The main centre-right opposition Social Democratic Party (PSD) allowed past austerity measures to pass in parliament by abstaining from voting. However it argues the new plan must be rejected because it hurts weaker members of society.

The PSD, which leads the ruling Socialists in opinion polls, says the government must be toppled so a new one can regain market trust.

Portugal is trying to squeeze its public sector deficit to 4.6 percent of gross domestic product this year, and then to the eurozone limit of three percent in 2012.

The public deficit hit a record 9.3 percent of GDP in 2009, the fourth-biggest in the euro region after Ireland, Greece and Spain.