About 2,000 retired teachers, many of whom are receiving pensions from the State, worked in schools last year, according to new figures supplied by the Department of Education.
These figures were supplied in response to a parliamentary question tabled by the Fine Gael education spokesman Brian Hayes.
Mr Hayes said the jobs should be given to new teaching graduates, adding that a graduate teacher recruitment scheme should be established.
Mr Hayes said a total of 1453 retired teachers were employed as substitutes in primary schools and the figure in post-primary schools was 368 during the 2008/2009 school year.
"Every hour of work, be it on a permanent or casual basis in a school, must be ring-fenced for those teachers who are currently looking for work," he added.
Minister for Education Batt O’Keeffe has sent a letter to all primary and second level schools "over the past number of weeks" urging principals to prioritise new graduates for both substitute and casual work, his spokesman said.
Incoming general secretary of the Irish National Teachers' Organisation (INTO) Sheila Nunan said the union had urged schools to ensure that newly qualified teachers were prioritised in terms of substitute work in schools.
"It is essential that unemployed teachers be given every opportunity to gain both classroom experience, and incremental and pension credit, from their service in schools," she added.
Last week, Minister for Education Batt O'Keeffe told the Dáil 1,500 teachers have retired this year at both primary and post-primary level.