“No more” can be done in some schools to save money, the head of the Education Authority (EA) has said.
Sara Long made the comments in a letter to all school principals in Northern Ireland.
She also acknowledged what she said was their “growing frustration” with a lack of adequate funding.
In July, a Westminster committee said a lack of money was having a devastating impact on schools in Northern Ireland.
Ms Long took up the post of chief executive of the EA in April 2019.
In her letter, she said principals and school leaders had been working in “challenging circumstances,” due to ongoing action short of strike by teaching unions.
More than 450 schools in Northern Ireland could not balance their books in 2019, according to EA figures.