Hospitals, shipyards and various transport hubs across Athens have been affected by the strikes, which mark the country’s first major industrial unrest of the new year.
The Athens metro, which is used by almost one million people every day, was shutdown in the strike, prompting traffic chaos in the capital.
The bill, set for parliamentary approval on Monday, would restructure family benefits, introduce a new process for foreclosures on overdue loans and make it more difficult to call a strike.
Angry locals marched through the capital, holding banners and chanting “hands off strikes!”
Protestors clashed with police outside the parliament building, who responded by firing teargas.
The draft law which is set to be approved by parliament next week has infuriated Greeks, who have seen their incomes fall and living conditions worsen since the Mediterranean country first sought international aid to stave off bankruptcy in 2010, and required another two bailouts thereafter.
Syriza, the dominant party in the government elected in 2015, has its roots in left-wing labour activism and its role in the new reforms has prompted widespread criticism from supporters.
Retired ship officer George Papaspyropoulos, said: “This essentially abolishes the right to strike… such things only happened during the junta,” referring to the military dictatorship that ruled Greece from 1967 to 1974.
“This government is a leftist in name only, but in deeds its a junta.”
At present, unions can call strikes with the support of one-third of their members. The new law would raise that to just over 50 per cent, which creditors hope would limit the frequency of strikes and improve productivity that lags about 20 percent behind the European Union average.
The government says it needs the reforms to receive tranches of bailout aid. The latest bailout, worth up to 86 billion euros ($104 billion), expires in August.
So far Greece has received 40.2 billion euros, and a new tranche is expected to be worth around 4.5 billion euros.