Mark Ramsankar says it will be difficult to find enough staff and resources for dozens of new schools promised by the government if spending is slashed.
Ramsankar says teachers are already concerned about lack of infrastructure and overcrowded classrooms.
He also says the union will be pushing to restart contract talks.
Teachers have faced a wage freeze for the last three years.
Ramsankar suggests the budgetary committee needs to come up with a better solution.
"It shows a real lack of leadership and responsibility on behalf of this government," he said Thursday. "Let's just cut. Let's just slash and burn this province."
Ramsankar says it's students who will be hurt in the long run.
"We will be looking at situations that students haven’t faced for many, many, many years,” he warned.
“They’ve talked about building schools for two years now and in many instances shovels still aren’t in the ground.”