Greece, which required three international bailouts between 2010 and 2015, has cut state pensions several times in recent years to make the system more viable
Traffic was gridlocked in parts of Athens on Tuesday as Greek transport workers joined a 24-hour public sector strike over pension reforms.
With the subway, trains and public buses at a standstill, many commuters were forced to drive to work, leaving major traffic arteries into the sprawling city of almost four million blocked.
Striking workers were expected to march to parliament around midday.
Greece, which required three international bailouts between 2010 and 2015, has cut state pensions several times in recent years to make the system more viable.
Draft legislation pending parliamentary approval creates a digital social security registry, and introduces more flexibility for the self-employed over contributions, delinking pensions from earnings.
Labour unions say the reforms are a thinly-disguised attempt by the governing conservatives to privatise pension funds, and accuse them of reneging on a promise to rescind all bailout-mandated cuts.
"The bill is nothing less than a continuation of the bailout laws that were voted in 2010-2019 and resulted in pension cuts of 20 percent up to 60 percent," ADEDY, the country's largest public sector union, said in a statement.