Greek high school teaching unions have voted to hold long-term strikes against public sector staff cuts ordered by the government as part of its bailout agreements.
The leader of the teaching union OLME, Themis Kotsifakis, said that union delegates voted overwhelmingly in favour of the weekly rolling protests starting next week.
The move represents the first major challenge to the country's conservative-led government over its programme to suspend 25,000 public servants this year and fire 15,000 by the end of 2014.
"Our answer to the (government) is a long-term strike that will take place in a decisive way. We are seeking the support of parents and other unions," said Mr Kotsifakis, who has been suspended from his state school teaching job.
Greece is stuck in a sixth year of recession, with the slump worsened by harsh austerity measures demanded by rescue creditors that have pushed unemployment up to more than 27%.
Conservative Prime Minister Antonis Samaras has promised to end the recession and return the country to bond markets next year after balancing the budget.
Latest Finance Ministry figures showed he was on the right track, with Greece beating its fiscal targets by a comfortable margin.
Teachers at state elementary and private school are also mulling possible strikes, while civil servants are planning a two-day strike next week.
Athens University staff has suspended all operations for one week in protest at the staff cuts. Other universities are considering similar action. Hundreds of administrative staff members held a protest march through central Athens, as did workers at country's General Mining and Metallurgical Company who were protesting at austerity measures that threaten their jobs.
Greece's international rescue lenders have not said how they will help make the country's national debt sustainable, and Mr Samaras' coalition government faces a tough midterm-test in the spring with municipal and European parliament elections. Polls suggest that Greece's anti-bailout parties are gaining ground.