A 24-hour nationwide strike disrupted transport and closed banks, schools and hospitals on Wednesday as trade unions protested labor reforms by Greece's conservative government.
Government offices, some banks, schools, post offices and hospitals were closed or operating a limited service.
Most transit services in the capital were also shut down, creating huge traffic jams in parts of the city - worsened by large downtown rallies staged by the strikers.
Also Wednesday, about 5,000 trade union protesters marched to the American embassy in Athens to demonstrate against the war in Iraq.
State carrier Olympic Airlines was operating a limited service with only one flight per destination, canceling dozens of other flights.
Some services by other airlines were delayed after baggage screeners joined the strike, said Marina Papageorgiou, a spokeswoman for Athens International Airport.
The strike was called by Greece's largest union, the General Confederation of Greek Labor, or GSEE, and the Union of Greek Civil Servants, or ADEDY.
Unions are angry at efforts to scrap protective job regulations in the public sector and argue that the collective wage bargaining process is being undermined by the government.
Prime Minister Costas Caramanlis' government has also promised to step up privatization of state enterprises.
Christos Polyzogopoulos, the GSEE leader, said the reforms have weakened job security and cut into spending power.
"This strike has had massive support and it sends a strong message: our tolerance has run out," he said. "Workers, the unemployed and pensioners - the vast majority of the Greek people - cannot bear these high prices, layoffs any more," he said.
The GSEE said strike participation in public sector was 90 percent, and 70 percent in parts of the private sector which had joined the strike.
Union officials said the strike had been called off in Greece's Evros region, bordering Turkey, after the area declared a state of emergency following major floods.
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The strikes are in keeping with a tradition of labor activism in the Greek capital on May Day, which is a public holiday.
The business plan will include privatizing a large part of the airline.