Updated

Chicago teachers and officials in the nation's third-largest school district will hold contract negotiations through the weekend in hopes of reaching a deal to avert a strike.

The Chicago Teachers Union has said its members are prepared to walk off the job as early as Tuesday. It would be the district's second strike since 2012, and affect about 400,000 students.

At issue are pension contributions, pay raises, staffing levels and classroom funding.

Chicago Public Schools officials argue the district faces massive financial challenges. Union officials say teachers don't want to strike, but are concerned about cuts to pay and benefits as well as school-level cuts that affect students.

CPS says school buildings will remain open if a strike occurs.