Just imagine your employer owes you thousands in back pay, or even tens of thousands. This employer had been shamed into giving you a pay rise by the EU, but three years later is still saying it cannot quite deliver on the promises.

When you protest, you are told there are lots of people like you, and the accounts department cannot figure out exactly how to give you your pay rise because it is terribly complicated. Then the employer throws you a few grand to shut you up, on which you pay 42 per cent tax. Quite frankly, you despair of ever getting what you have earned.

What am I describing? Desperate immigrants brought in on a work visa held by an employer who is banking on people being too terrified of deportation to protest? No, it's the situation of thousands of non-permanent teachers at post-primary level, who are employed by the Department of Education and Science. Yet if you asked these teachers what they wanted, their back money would be second on the list. At the top would be a permanent job.

Some of them have worked for five, 10, or even 20 years, and are still waiting to see the magic word "permanent" on a contract. So many fine teachers have left the profession because they just can't hack the insecurity any longer. Picture not knowing in August whether you will have a job in September, and if you do, what subjects and how many hours you will have. Imagine how vulnerable such people are. A permanent teacher has a degree of status that allows her or him to refuse unreasonable requests. A non-permanent teacher feels perpetually on probation, and is unlikely to be in a position to refuse anything. Not to mention that non-permanency makes securing a mortgage next to impossible.

Think about the unfortunates who are still working as substitute teachers after years, for a few weeks here and a few weeks there. Teaching is tough enough when you are established in a school. Imagine facing the ingenious tortures devised by teenagers for new teachers, again and again during a school year. The amazing thing is not that so many non-permanent teachers have left the profession completely, but that any of them stay.

Some teachers are non-permanent because numbers have fallen in the school, and the Department won't sanction a permanent post. However, it goes on sanctioning non-permanent contracts, or hours, because the school couldn't provide a full service to students without them.

It is all an unholy mess. Take back pay, for example. In December 2001, the Government legislated to comply with an EU directive on part-time workers that declared they were not to be disadvantaged compared with full-time colleagues.

As a result, the Department created three new categories of non-permanent teachers at post-primary level. The first is those who are contracted for a full school year, no matter how few their hours are. Then there are the teachers who are teaching more than 150 hours in a year, but who are contracted for less than a full year. Finally, there are the people who are employed on a casual basis, for less than 150 hours in the school year.

Extraordinarily convoluted? Well, yes. Yet it was hailed as a major innovation, because the first two categories were to be paid by the hour, according to what their salaries would be as a whole-time teacher. In justice, every teacher should be entitled to this, but the third new category, so-called casual teachers, are still paid far less than everyone else.

The back pay arises from the discrepancy between what should have been paid and what is actually paid. Even now, non-permanent teachers continue to wait for what they are owed. The Department's excuse is that there are 2,574 regular part-timers (not counting those doing casual hours) in secondary, community and comprehensive schools alone. Figuring out exactly what rate per hour people should receive by taking into consideration qualifications, how long they have been teaching and for how many hours, is very complex. They never mention they have known since at least 1999 that this was coming.

There are serious amounts of money involved. One teacher was owed more than €34,000 by June 2004. There are many more owed greater and lesser amounts.

When the Department kept stalling about paying up, the unions hammered out a deal on an interim payment, to soften the blow of the delay of full payment. Teachers are supposed to see this interim payment as progress, instead of a sop. It is hard to imagine another profession where people would go on working, being given continually broken promises. The unions bear some responsibility, by not being able to agree on what should constitute an increment, but more importantly, for not giving enough support over the years to non-permanent teachers.

One of the nastier ways it saves the Department money to employ so many teachers on a casual basis is because a teacher contracted for less than a full year is not entitled to sick leave.

I know teachers who will drag themselves to school in a half-dead condition, because they feel they cannot afford to take time off. It is outrageous. By the Department's own admission, it concerns thousands of teachers. How much longer will this be allowed to continue?

Breda O'Brien is a secondary teacher in Muckross Park College, Donnybrook, Dublin and a columnist with The Irish Times