School guards that are to be placed in labour reserve in August placed their uniforms on top of Greek flags lying on the ground in front of riot police in a symbolic gesture.
The bill - whose passage is a condition for Greece to unlock further aid from the EU and the IMF - includes plans for a public sector transfer and layoff scheme mainly affecting teachers and municipal police.
Greece's coalition government scraped through a vote late on Wednesday on a bill to sack public sector workers as thousands chanting anti-austerity slogans protested outside parliament.
The vote was the first major test for Prime Minister Antonis Samaras's two-party coalition since losing an ally over the closure of the state broadcaster last month, which left it with a small five-seat majority in the 300-seat parliament.
After midnight on Wednesday, 153 lawmakers out of the 293 present voted in favour of the bill, whose passage was required to unlock nearly 7 billion euros (£6 billion) in aid from European Union and International Monetary Fund lenders.
The bill includes deeply divisive plans for a transfer and layoff scheme for 25,000 public workers - mainly teachers and police - that had triggered a week of almost daily marches, rallies and strikes in protest.