CHICAGO — The Chicago Teachers Union on Wednesday threatened to strike if no agreement is reached on a contract with Chicago Public Schools by Oct. 11.

Saying it’s time to move contract talks along, union president Karen Lewis said teachers will “withhold our labor” if an agreement isn’t reached to replace a contract that expired more than a year ago.

The union’s approximately 25,000 members walked out in 2012 for 10 days and staged a one-day walkout in April.

Although a strike date has been set, teachers can opt to stay in the classroom if talks show progress. Lewis wouldn’t say if the sides are close to an agreement.

Before the union announced its deadline, the cash-strapped Chicago Board of Education authorized a $15 million emergency plan to shelter and feed students if teachers walked off the job.

Union vice president Jesse Sharkey said in addition to pay, the union’s stance is partially motivated by cuts in school staffing, including librarians, and services such as special education experts.

“We will continue to listen, continue to negotiate and continue to do everything possible to avoid an interruption to our students’ learning,” schools CEO Forrest Claypool said. “A strike would harm the children we’re all here to serve.”