ATHENS, Greece (AP) -- A union representing teachers at Greek state high schools on Friday called a series of strikes to start next week over new austerity cuts, an action that threatens annual university entrance exams.

The Greek Federation of Secondary Education State School Teachers, OLME, voted to hold a 24-hour strike on May 17 and rolling strikes the following week to protest government plans for involuntary staff transfers and longer working hours. The measures are part of a shakeup of the public sector sought by the country's emergency lenders.

The conservative-led government has said it will take action to make sure the May 17-31 exams for school leavers and university candidates, but has not said whether it will challenge the protest in court.

Greece is locked in a harsh austerity program, demanded in exchange for the international rescue loans that have kept it afloat since 2010. But the conservative-led government says the program is making progress, with the country's first-quarter budget deficit falling to less than half the sum initially forecast.

Deputy Finance Minister Christos Staikouras said the government overspending in January-April 2013 reached 2.45 billion euros ($3.22 billion), against a targeted 5.74 billion euros ($7.54 billion).

Preliminary data reported Friday set the primary deficit -- which excludes the cost of servicing Greece's massive debt -- at 330 million euros for the quarter, less than a tenth of the anticipated 3.61 billion euros.

For the first time this year, tax collection was on target in April, while quarterly net revenues were 5.1 percent above target.

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