The growing trend of teachers being offered fixed-term contracts instead of permanent work needs to end, says the Post-Primary Teachers Association (PPTA).
New research presented at a PPTA conference shows an increase in the number of schools breaching the Employment Relations Act. It has strict limits on the use of fixed-term contracts.
Angela Roberts from the Post Primary Teachers' Association says it's lowering teachers' moral and commitment to their jobs.
"When they're not being committed to by the system, it makes it harder for you to commit to the system, to ride out the rough days and those sorts of things."
Only 15 percent of teaching graduates go into permanent roles when they finish their studies, according to the paper. The rest are being forced into the "precariat" - a growing social class defined by their lack of permanent employment.
Ms Roberts says a lack of funding is adding to the problem.
"This is one way that school try and better manage their funding. Some schools illegally trial teachers to check them out for a year. We don't have a 90-day trial - we have a year-long trial."
The PPTA is concerned the Education Review Office (ERO) isn't on board in correcting the issue.
"I haven't heard ERO say that they're interested in ensuring that boards are ethical employers," says Ms Roberts.
The paper says schools are also worse off, with the high staff turnover caused by fixed-term contracts having a negative impact on institutional knowledge.
Teachers recently voted against backing the Government's proposed shake-up of school funding.