The key case will be heard by the Labour Court in March.

Eileen McEvoy, a commercial and secretarial teacher, argued at the Equality Tribunal that new legislation introduced in 2004 should have allowed her to re-apply for her position.

That legislation provides that all public servants recruited after 2004 can go on working past the age of 65. In a concession to serving public servants once they reach 65, they can re-enter the public service as a 'new entrant', although they must wait 26 weeks before they can take up the job.

McEvoy told the tribunal that Mount Temple did not inform her that it had advertised her position six months before she reached the age of 65. She said that, as she was not afforded the chance to apply for her job, this amounted to age discrimination.

Mount Temple said it was informed by the Department of Education that McEvoy was due to retire in August 2004. It said it was obliged to fill the position and could not have waited for 26 weeks.

Equality officer, Geraldine Coyle, ruled that the school was following instructions from the department and did not discriminate against McEvoy. She declined to comment on McEvoy's plans.

Niall Crowley, chief executive of the Equality Authority, said in the last six months the authority has witnessed a "significant increase" in the number of age discrimination allegations, the vast majority concerning the mandatory retirement age.

While EU equality laws - including Ireland's Equality Act 2004 - outlaw age discrimination, a controversial exception allows employers to set mandatory retirement ages.

The UK High Court last month referred a claim against the mandatory retirement age to the European Court of Justice. Crowley said the authority would be keeping "a very close eye" on that case as it would impact on retirement ages here.