Thousands of protesters are taking part in an annual march in the Greek capital, Athens, with numbers swelled by anti-austerity demonstrators.
The rally marks the anniversary of a student uprising in 1973 that helped bring down the country's military dictatorship.
There was a brief clash outside the parliament when police fired tear gas at youths throwing petrol bombs, but the march has been mainly peaceful.
Some 7,000 officers are on the streets.
Analysts say it is the first test of public defiance against Prime Minister Lucas Papdemos's new government.
It comes a day after Greece's interim government won a confidence vote.
Mr Papademos's governing coalition had a huge majority - 255 MPs voted in favour, and 38 against.
His technocrat government must approve a new bailout package and commit to reforms in order to secure the next instalment of an international loan.
The 17 November demonstration traditionally draws huge crowds in Athens every year.
People march from the polytechnic to the US embassy in protest at US support for the military junta, which Washington saw at the time as a buffer against communism.
But this time the march is imbued with a lot of anger about the austerity measures, says the BBC's Mark Lowen in Athens.
In 1973, the uprising helped usher in the end of the country's then leadership, and the current government is hoping that history will not repeat itself, our correspondent adds.
The government says the austerity measures are essential, although two party leaders within the coalition remain reluctant to sign a document committing themselves to the bailout terms.
They are the leaders of the conservative New Democracy party, Antonis Samaras, and the leader of Greece's Far Right Laos party, George Karatzaferis.
But both leaders backed the unity government in the vote.
Mr Papademos, an unelected former banker, earlier said his priority was ratifying the international 130bn euro ($177bn; £111bn) bailout package agreed at an EU summit last month.
Speaking before Wednesday's confidence vote in parliament, Mr Papademos appealed for unity and said Greece needed to take bolder steps to tackle the crisis.
"Dealing with Greece's problems will be more difficult if Greece is not a member of the eurozone," he told parliament.
The planned reforms have already triggered widespread protest in Greece.
The crisis led to the resignation last week of the then-Prime Minister George Papandreou.
The unity government is intended to run the country until elections in February.