Denver Public School (DPS) teachers will begin a strike on Monday over failed negotiations over compensation.

The Denver Classroom Teachers Association (DCTA) announced Saturday that they would begin striking for the first time in 25 years.

“Teachers were stunned when DPS proposed hiking incentives instead of putting that new money into base pay where it could make the entire district more competitive,” DCTA President Henry Roman said. “We are incredibly disappointed that on the last day of bargaining and less than two days before a strike, they doubled down on one-time incentives teachers do not want, and the data shows do not work to keep teachers in their schools.”

{mosads}“We will strike Monday for our students and for our profession, and perhaps then DPS will get the message and return to the bargaining table with a serious proposal aimed at solving the teacher turnover crisis in Denver.”

The DCTA and Denver Public Schools have been negotiating a wage increase for 15 months. The Denver Post reports they negotiated for six hours on Saturday with minimal progress.

District officials, who have hired 300 new substitute teachers in addition to their current rotation of 1,200 subs, plan to keep schools open during the strike.

While the district is planning to use subs to keep schools open, they have canceled classes for the roughly 5,000 preschoolers in the area because of staffing shortages.

“We presented an updated proposal that responds to what we heard from our teachers, aligns to our values of equity and retention, honors the ProComp ballot language and significantly increases the base pay for all of our educators,” Superintendent Susana Cordova said in a statement, per the Post.

“Despite the union’s refusal to continue negotiating, we remain committed to working with the leadership of the DCTA to end this strike.”

The Professional Compensation System for Teachers, or ProComp, was established in 1999.

That system expired on Jan. 18 amid arguments over base teacher pay and funding allocation.

DCTA is proposing a package of $28.5 million for teacher compensation, while the district was offering $23.3 million as of Saturday night, according to ABC Denver affiliate KMGH.

DCTA has advocated funding higher base pay by lowering bonuses paid to teachers at high-poverty schools.

DPS says those incentives are key to improving performances of poor and minority students.