Today's announcement of a general strike came after Greece's parliament said the government's pension and taxation reform bills would be debated and voted on this weekend.
Changes to Greece's pensions system were demanded by creditors as a condition of the country's third bailout in five years, worth 86 billion euros (USD 95 billion), agreed in July last year.
Parliamentarians will also debate whether to increase taxes on high and middle-income earners.
The powerful PNO seafarers union meanwhile called for a four-day strike from early Friday morning to Tuesday morning which could paralyse ferry services between Greece's islands and the mainland.
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The GSEE private sector workers' union told the government to prepare for a "permanent fight" if it did not back down over the reforms.
Marches are expected in Athens and other cities this weekend and will coincide with celebrations for International Workers' Day this Sunday which were postponed from May 1 owing to the timing of Orthodox Easter.