A majority of lawmakers voted in favour of the bill which paves the way for PPC to begin selling plants in May. It is a requirement of a multi-billion euro bailout accord between Greece and international lenders.
Hundreds of PPC workers gathered outside parliament as lawmakers debated the legislation earlier on Wednesday, urging them not to allow what they said was "a fire-sale of the family silver".
"Privatising PPC means fewer jobs, lower wages," said Spyros Nikolopoulos, 54, a PPC worker for 32 years. "PPC belongs to the Greek people, it cannot be sold to any private investor."
The conservative opposition accused the government of bringing PPC "to the brink of disaster" and lying to its voters. But Energy minister George Stathakis defended the sale as complying with the European Union's target to cut power generation dependence on coal in the coming years.
"Coal's weight (for PPC) has decreased and will continue doing so, because all the units that will be sold will not be replaced," Stathakis told lawmakers.
"So all this talk that PPC's silver will be gone has no point."
Some of the protesters emptied sacks of coal outside parliament.
Greece is implementing reforms and asset sales in exchange for loans from the European Union. It has agreed with its lenders to sell 40 percent of the coal-fired capacity of PPC, which is majority state controlled.
A coal fired unit and a licence for a second in Florina, northern Greece, will be sold along with two units in southern Greece. Under bailout terms, PPC should launch an international tender for a buyer at the end of May.
The country will divest the capacity to comply with a European court ruling which said that PPC had abused its dominant position in the dirty but cheap coal market.
EU competition regulators which put out feelers for interest in the asset in a so-called 'market test' got interest from fifteen investors, PPC said.,
Wednesday's protest was organised by PPC's most powerful union GENOP-DEH, which kicked off rolling strikes this week.
(Reporting by Lefteris Papadimas and Angeliki Koutantou; Editing by Toby Chopra and Alexandra Hudson)