The proposal — likely signaling an austerity contract and rough bargaining to come — was denounced by a “highly insulted” union.

CTU President Karen Lewis, who led her members to strike in 2012 for the first time in 25 years, accused CPS of being “broke on purpose” and of retaliating against the union for opposing the mayor in his recent re-election campaign.

“Once again, the board has created a fiscal crisis in order to justify its continued attack on our classrooms and communities. By citing its so-called $1.5 billion deficit, the mayor is proposing a reduction in teaching staff which will result in larger class sizes and the loss of teaching positions,” Lewis said in a press release.

“The CTU is highly insulted,” said union spokeswoman Stephanie Gadlin, who planned a press conference on Wednesday.