Relations between the Government and striking secondary teachers plunged to a new low last night, with the Taoiseach accusing them of abandoning students in the run-up to exams.
However, in a fresh blow to the Government's contingency plans for the exams, third-level students were told not to take part in correction and supervising of this year's Leaving Cert.
The president of the Union of Students in Ireland (USI), Mr Julian de Spainn, said the Government's plans were "riddled with flaws".
He said he did not want students to be "scapegoated" if questions were asked about the validity and integrity of the exams.
Mr Ahern said there was no point in meeting the ASTI because of its present stance. In a strongly-worded letter, he said there was no basis for direct negotiations.
He said ASTI appeared to be willing to abandon exam students. "Your association may feel able to abandon the students in this predicament; the Government will not."
He said the Government had a responsibility to hold public exams and he could not understand why teachers were preparing to jeopardise them.
"We cannot understand how teachers, in conscience, can contemplate jeopardising the future careers of many students for whose education they are responsible, particularly in view of the increases that they have received to date and those now on offer through the implementation of Labour Court recommendations."
Mr Ahern also criticised ASTI for not balloting its 17,000 members on the Labour Court recommendation. "To embark on this course without reference to a ballot of the membership, having regard to what is at stake, is truly remarkable."
Last night, the ASTI standing committee discussed yesterday's one-day strike. One member said: "We are more resolute than ever. But the Government will probably let us sweat it out for another fortnight, at least."
The committee heard that some ASTI members had - in correspondence with the union - expressed concern about the plan to hit exams. However, reports from various regions showed widespread support for the union's stance.
The committee was also told the union appeared to be protected from any potentially costly legal actions by parents or others.
In other developments, the Labour Party called on the Minister for Education, Dr Woods, to resign because of his handling of the strike. The party's education spokeswoman, Ms Roisin Shortall, said Dr Woods should go over his "gross mishandling" of the dispute.
She said as long as Dr Woods remained Minister the chance of a solution would diminish. "The extraordinary decision of Minister Woods to travel to Malaysia and Singapore, despite the huge crisis now facing second-level students, is the last straw as far as many parents are concerned."
Fine Gael is to use its time in the Dail next week to hold a debate on the Government's handling of the dispute. Its education spokesman, Mr Michael Creed, said: "The only useful contribution the Minister for Education can come up with in this crisis is to travel to Kuala Lumpur to meet the Malaysian Minister for Education. This speaks volumes about the Government's priorities where public relations events take precedent over issues of urgent national interest."
At their spring meeting in Maynooth, the Irish Catholic bishops expressed concern for the young people affected by the dispute. They appealed to all parties to give "particular consideration" to the plight of students facing the Leaving Cert who were "at a crossroads in their young lives".
The bishops said a serious injustice might be done to students unless an adequate accommodation for them was arrived at quickly.