(CBS) — The first strike in Prospect Heights School District 23 ever could happen this week.

Teachers are asking for $1.3 million in raises over the next three years, but the district says school officials would have to borrow money to pay those salaries.

The current contract expired at the end of June and the two sides have been negotiating.

Teacher Jodi Hernandez says the union has put up four different offers but the district won’t budge. She says they voluntarily agreed to a pay freeze a few years ago to help with financial problems but now it’s time to pay the piper.

“We have helped out as much as we can. We funded a lot of things in our school district on our backs, and we’re just trying to recoup what we lost,” Hernandez says.

A strike would affect about 1,600 students in pre-K through 8th grade at four schools in Prospect Heights.

If it happens, the district says their pool of substitute teachers isn’t large enough to cover all the classrooms.