Greek police have used tear gas on protesters throwing petrol bombs outside parliament in central Athens as Greek lawmakers debated controversial tax and pension reforms inside.
The reforms, which will cut the amount of money given to 7.5 per cent of pensioners, were agreed by Greek Prime Minister Alexis Tsipras in order to unlock further international bailout money needed to keep Greece afloat.
But they are unpopular with the Greek people, who turned up in their thousands to protest.
Some 18,000 people are said to have turned up in Athens and another 8,000 in Thessaloniki on Sunday, police said. Police used tear gas after petrol bombs were thrown.
Parts of central Athens were closed to traffic and police presence increased in the city, although the protests were smaller in scale than those in February.
The reforms include reducing Greece's highest pension payouts, merging several pension funds, increasing contributions and raising taxes for those on medium and high incomes.
They are part of a package demanded by Greece's European creditors, the IMF and the EU, in exchange for $95 billion in bailout funding approved last July.
Greece also agreen to hike VAT and put measures in place to automatically cut spending if it fails to hit suplus targets.
The IMF is trying to force Greece to put in an additional €3 billion in contingency measures in case the agreed cuts are not enough to meet the programme's budget surplus targets.
Athens reportedly said it was "politically impossible" to legislate for such a plan.
Eurozone officials have said the rift between the IMF and Greece on this point could jeopardise the agreement to release the bailout money at a meeting of ministers in Brussels on Monday.
Greece must secure €3.5 billion in time to a debt repayment in July. On Monday, ministers will discuss for the first time the possibility of granting debt relief to Greece.
The governing Syriza party has long demanded debt relief in return for sweeping austerity measures but this is the first time that it has been tabled for talks after the IMF said that the Eurozone must consider reducing Greece's debt.
