Athens public transport was disrupted for five hours on Monday in the buildup to two 24-hour strikes on Wednesday and Thursday that will also affect hospitals, banks and the civil service.
The protests, called by Greece's two largest labor unions, target a draft law by the governing conservatives designed to overhaul the country's ailing public corporations and eventually end assured jobs for life for new employees.
"The draft law is unconstitutional and goes against workers' rights," the GSEE umbrella union said. "GSEE and public corporation unions strongly oppose this proposed legislation."
GSEE is particularly incensed by a clause that will allow changes to work terms in loss-making public corporations.
On Monday, GSEE staged a protest march through central Athens to Parliament - which will start debating the draft law on Tuesday - adding to the congested city's traffic woes. Matters were made worse by a five-hour public transport strike.
On Wednesday and Thursday, nearly all public transport networks will be closed down all day, with only the metro and urban rail providing services from 0900 to 1600GMT on Wednesday.
Workers at hospitals, banks and all public sector departments will be on strike on Wednesday, as well as private sector employees.
Public corporations and utilities will be on strike both Wednesday and Thursday.
The government took a first step toward curtailing civil servants' considerable privileges - public sector employees enjoy assured jobs for life - earlier this year, after striking a deal with workers at Greece's largest telecoms operator, the AP reports.