   It is the third time this year that Prime Minister Antonis
Samaras's government has invoked emergency law to force strikers
back to work to try to show foreign lenders who bailed out
Greece that the country is sticking to unpopular reforms.    It
has called for a 24-hour strike when exams start on 17 May and
rolling strikes the following week.    OLME plans to hold a
rally in central Athens on Monday and called on the main public
and private sector unions, representing about half the country's
workforce, to stage a general strike in solidarity on 17 May.
Education Minister Constantine Arvanitopoulos said banning the
strike was necessary because students had a "sacred right" to
sit exams without disruption.  The main opposition has called on
the government to withdraw the law and open dialogue with the
teachers after the exams.  "These threats by the prime minister
and his government are directly against the overwhelming
majority of workers and society," the Syriza party, which
opposes the country's bailo