Thousands of Greek workers walked off their jobs Wednesday, shutting down public services in a massive protest against government austerity measures aimed at securing more international aid for the debt-ridden country.

The 24-hour strike called by Greece’s two major unions shut schools, courts, local and national governmental operations, and forced the cancellation of more than 400 flights at the Athens International Airport. The workers were protesting Prime Minister George Papandreou’s latest deficit-cutting plan to trim pensions, while cutting the pay for 30,000 civil servants and then eliminating their jobs.

Some demonstrators in Athens hurled rocks at police, who fired tear gas at them.

Greece’s international creditors have demanded that the austerity measures be imposed in exchange for handing the Athens government another segment of last year’s $159 billion bailout. But the austerity measures have proved highly unpopular with Greeks, who staged smaller work stoppages before Wednesday’s much larger street demonstrations in the Greek capital and the northern city of Thessaloniki.

Greek Finance Minister Evangelos Venizelos said Tuesday the country is dependent on continued international assistance, and must make “superhuman efforts” to meet the demands of its creditors. He said, however, that while the government has approved the austerity measures, Greek society has “not taken a clear decision” on them and that the country is “hostage to great contradictions.”

Demonstrators said they did not want to lose their jobs or have their pay reduced as a part of the expanding austerity measures. A new, equally unpopular property tax has also been imposed.

Some blamed wealthier European neighbors and Greek authorities for their plight. Protesters shouted at riot police in Athens that they were “employees of Merkel,” a reference to German Chancellor Angela Merkel, the leader of Europe’s biggest economy and a supporter of the Greek austerity measures.

The European Union, the International Monetary Fund and the European Central Bank are trying to decide whether to release a $11 billion installment of last year’s bailout, while European leaders are also reconsidering the terms of a second Greek bailout they approved in July. Before releasing the funds from last year’s bailout, Greece’s creditors are insisting that the country significantly cut its deficit even though the government acknowledged it will not be able to meet the terms it agreed to just three months ago.

Greece said Sunday that it will miss its government deficit reduction goals by nearly one percentage point.