Tens of thousands of public sector workers have gathered in the Romanian capital Bucharest to protest against plans to cut wages and pensions.
"We will not leave until the government quits," said Bogdan Hossu, leader of the Cartel Alfa trade union.
The government has proposed wage cuts of 25% and pension cuts of 15% in order to reduce the country's budget deficit.
Romania's economy shrunk more than 7% last year and it needed an IMF bail-out in order to meet its wage bill.
It says it needs to implement new austerity measures to qualify for the next instalment of the 20bn-euro ($25bn; £17bn) IMF loan.
Protesters began gathering at the capital from early morning on Wednesday. Police put the number present at around 30,000, while the unions said it was 50,000, according to the AFP news agency.
Many of them arrived from other parts of the country by bus and police blocked a number of streets in the city to maintain order.
The gathering was one of the biggest on the streets of Bucharest was one of the biggest since the Romanian Revolution.
Marian Gruia, head of the policemen's union, called on Romanians to unite, "as we did in 1989, when we overthrew the dictatorship" of communist leader Nicolae Ceausescu.
Demonstrators carried banners criticising the centrist government of Prime Minister Emil Boc and President Traian Basescu.
Mr Boc was re-appointed in December after being forced out when his coalition collapsed in October.
Mr Basescu has said cuts to Romania's huge public sector - which accounts for a third of all jobs - are preferable to tax rises.
But analysts and investors apparently fear the government may lose its nerve and cave in to the protesters. An auction of government debt earlier this month failed to attract enough interest.
Economy ministry official Marcel Hoara was booed and sprayed with water and stones after joining a live televised debate in the middle of the protest. Police escorted him from the area.
Unions are threatening a general strike later this month if their demands are not met.