Greek riot police fired tear gas to disperse stone-throwing demonstrators Tuesday, as thousands marched to protest proposed austerity measures on the first day of a two-day strike.

Police fired tear gas canisters into the crowds as protesters threw rocks at security forces.

One protester and three police officers have been slightly injured, the police said. About 3,000 officers are deployed on the streets of Athens.

The protesters are rallying outside the Greek Parliament building in the center of the country’s capital, where lawmakers are set to vote Wednesday on a tough five-year package of tax increases and spending cuts.