CHICAGO – The Chicago Teachers Union and district officials said they will negotiate through the weekend, if necessary, to try to avoid a strike on Monday. Teachers are ready to walk off the job for the first time in 25 years over issues that include pay raises, job security and teacher evaluations.

There is a lot riding on this contract for Mayor Rahm Emanuel, who has made school improvement a central theme of his administration, and for the teachers union, which feels its ability to protect teachers and give them a voice in education is under attack.

Both sides said Friday that they were optimistic that a contract could be settled without a strike, though a union spokeswoman said they remained “far apart” on issues such as job security and pay.