At least 2,500 teaching and support staff posts must be axed by April, or the number of job losses will be doubled, it has been warned.
The Department of Education's finance chief Trevor Connolly has revealed that if 1,000 teachers and 1,500 non-teaching posts are not cut by April, even more posts must go to realise the savings they need to make.
A leading teachers' union has blasted the target as "impossible".
Justin McCamphill of the NASUWT said the losses of so many teachers in addition to workloads being increased by the departure of even more support staff will devastate schools during the stressful pre-exam time.
The Department of Education has to make cuts of £198m to its budget for 2015/16.
Briefing Stormont's Education Committee yesterday on how they plan to do this, Mr Connolly explained that the schools' maintenance budget and minor works scheme has been disproportionately cut in a bid to minimise the effect on front line services.
However, he pointed out that more than 75% of the education budget is spent directly on salaries or salary-related costs, so protecting these completely is "undeliverable".
Mr Connolly described the situation as "bleak" and "extremely difficult" as he explained why the posts must be cut by April.
"If people go at the start of April, you get a full year's saving from that person's salary," Mr Connolly told the committee.
"If that person goes by September 1, that means you have paid that person's salary for five months, then you have to find that saving. Then we would have twice as many people losing their jobs.
"That's why the minister wants to have that discussion with trade unions now, that's how you can minimise job losses."
Schools across Northern Ireland received letters from the Department earlier this week requesting that they plan for these savings.
Mr McCamphill commented: "I think what they are going to find is that it is not possible. We were shocked as we had been working on the assumption that it would happen in August. This is going to cause devastation in schools."
He continued: "There are going to be boards of governors who, coming up to Christmas, are going to have to start looking at making people redundant.
"We are worried about the impact this is going to have on our schools, particularly on the kids preparing for their exams, if teachers have to leave in April."
The union chief said there may be compulsory redundancies as voluntary ones will not be an attractive prospect for many. Last year, just 400 teachers applied for a voluntary redundancy scheme.
Mr Camphill and the other trade unions were informed of the proposed job cuts in a briefing on Tuesday.
He said it was too early to know if members would be seeking industrial action. However, another union, the Irish Congress of Trade Unions (ICTU) which represents non-teaching staff, has indicated they may be taking part in industrial action.
The Department of Education is currently consulting on its draft budget proposals. The closing date for submissions is December 29.