Riot police fired tear gas to disperse a group of rock-throwing youths during a demonstration Tuesday in support of a nationwide general strike that brought air, rail and ferry traffic to a halt in Greece.

Public offices shut down across the country as workers walked off the job to protest the conservative government’s economic policies. Hundreds of thousands of Greeks took part in the 24-hour general strike, according to GSEE, the country’s largest umbrella union.

Thousands of people marched through central Athens in two separate demonstrations. While the first march of about 15,000 people was calm, clashes broke out during the second march between riot police and groups of youths throwing rocks and other objects at store windows.

Police fired tear gas, sending the demonstrators scurrying for cover. There were no immediate reports of any injuries.

Across the country, state hospitals functioned with emergency staff while state schools, universities, post offices and tax offices were closed, as were many banks.

Some 200 domestic and international flights were canceled while all ferries were confined to port and the state railway company canceled most train services.

Lawyers, journalists and civil engineers were also on strike.

“The country has effectively come to a halt,” said union spokesman Efstathios Anestis. “Participation is very high, in many sectors it exceeds 90 percent of the work force.”

GSEE, which covers the private sector, and civil service umbrella union ADEDY called the strike to protest recent legislation reforming the country’s fragmented pension system. The new law, passed in March, cuts back early retirement rights and merges lucrative pension funds with financially troubled ones.

“We’re expressing anger, despair and rage about the policies which give to the few,” said GSEE leader Yiannis Panagopoulos.

The two umbrella unions represent some 2.5 million workers between them, or about half of Greece’s total work force.