Striking public transport workers halted Athens's buses, trams and metro for six hours on Tuesday in protest against the austerity measures being introduced to tackle Greece's debt crisis.
A new opinion poll indicated 61 per cent of Greeks were opposed to the government's decision to ask for European Union/International Monetary Fund (IMF) aid - a measure that is likely to entail even tougher cuts in public spending.
On Monday striking dockworkers blocked hundreds of tourists from returning to their cruise ship.
After weeks of refusing to trigger a 45 billion euro ($60 billion) aid package, the government bowed to market pressure on Friday and asked to activate it.
The public outcry has unnerved some investors, who fear reform efforts may take a hit if it grows into unrest on the lines of the riots that paralysed Athens for weeks in December 2008.
"We denounce the anti-popular and anti-labour measures of the government," the public transport federation OSME (Federation of Transport Unions of Greece) said in a statement, opposing plans to raise the retirement age and cut pensions.
The government has said it will increase the average effective retirement age to 63, from 61, but Greek media say the IMF wants a bigger increase.
The Socialist administration has already cut public pay and raised taxes, moves that have already sparked strikes and demonstrations over the past month.
"I am determined to do whatever it takes, when it is needed, to revive our country," Prime Minister George Papandreou told his parliamentary deputies on Tuesday.
"It's now or never - but we will succeed."
The Confederation of Public Servants, ADEDY, was due to stage a protest march in Athens at 1500 GMT, and the umbrella private sector union GSEE is expected to decide soon on a strike in early May.
"The government's resorting to the IMF support mechanism signals a barbarous attack on workers' rights," ADEDY, which represents half a million workers, said in a statement. "We, the workers, will continue and escalate our struggle against the anti-popular measures of the government, the EU and the IMF."
According to an opinion poll, published late on Monday, 67.4 per cent of the 1,400 people surveyed thought the current situation could lead to social unrest, against 30.4 per cent who believed it was probably or totally unlikely.
Only 31.9 per cent thought the PASOK government should stay in power to solve the crisis, while 31 per cent were in favour of a national unity government between PASOK, New Democracy and a far right party, according to the poll by Greek Public Opinion (GPO) for Mega TV. Another 27 per cent liked neither option and 10 per cent had no answer.
Nevertheless, 50.8 per cent approved of Papandreou's performance as Prime Minister.
The premium investors demand to buy Greek government bonds rather than euro zone benchmark German Bunds hit 687 basis points on Tuesday, after a German budgetary expert suggested aid to Greece could still be blocked. It was the highest level since Greece joined the single currency.