Greek workers call one-day strike May 20

Public and private sector unions had initially called a strike for May 19, but decided later on Wednesday to move the walkout a day later, saying they did not want to hinder national university entry tests on the same day.

Unionists have vowed to stop the pension reform, a key condition in a financial rescue plan for Greece agreed last week with the euro zone and the International Monetary Fund (IMF).

The country's socialist government unveiled a draft law on Monday that raises the average retirement age and pares back benefits to plug the pension system's ballooning deficits.

"The IMF will not stop thirsting for workers' blood," said Yannis Panagopoulos, chairman of Greece's main private sector labour union GSEE. "Its recipes are a disaster and the government must turn them down."

The walkout is expected to ground flights to and from Greece, disrupt transport and shut down ministries and public services across the country. The unions will convene after the strike to decide on future action.