"No to salary cuts!" read one banner held up by the protestors, civil servants from across the country, AFP reported.
They were protesting the reduction of some 125,000 civil servants by 2016, part of a new austerity package that squeezed through parliament on Wednesday, with just 153 lawmakers voting in favor of it in the 300-member chamber.
On Saturday, lawmakers began the debate on the 2013 budget on which they are due to vote late on Sunday in the second key test for the government in less than a week.
The 2013 budget predicts that the economy will shrink by a worse-than-previously expected 4.5 percent next year and that the country's debt mountain will swell to 346 billion euros ($450 billion), or 189 percent of economic output.
The government is planning 9.4 billion euros ($12.2 billion) in cuts which will affect mainly state wages, pensions and benefits that have already been drastically reduced over the past two years.
But it will still need to borrow over 68 billion euros next year, the draft budget says.
Greece is currently surviving on two huge bailout packages from its troika of creditors, the European Union, the International Monetary Fund and the European Central Bank.
In return for the aid to avoid default, Athens has introduced a series of austerity measures which have sparked popular anger in a country that faces a sixth year of recession and where unemployment hit above the 25 percent mark in July.