Barnaby Phillips, Al Jazeera's correspondent in Athens, said the gathered crowd gathered appeared to be smaller than in other general strikes.
"Whether that's because people are simply exhausted by these endless protests, whether that's because there's been no public transport at all today ... or whether more people are coming around to the government's point of view, is all conjecture at the moment."
But he said despite the reduced numbers, the atmosphere was still tense.
The latest reform bill is an important condition for an austerity deal agreed with the European Union and the IMF in return for a $138.6bn aid package to pull the country out of a severe debt crisis.
Politicians agreed in principle on the reform in a preliminary vote late on Wednesday.
Analysts see it as a major test of the government's ability to push through structural reforms.
Many Greeks are angry with the prospect of having to work longer for a smaller pension, particularly women who can now retire as early as 55.
"It's horrible, we paid all our contributions, we paid our taxes, and we are not going to get anything," Vaso Spoulou, a 54-year-old protester, told the Reuters news agency.
"They are destroying everything."
Previous demonstrations this year have turned violent, and on May 5 three employees died trapped in a bank set on fire by suspected anarchist rioters.