CHICAGO - The Chicago Teachers Union (CTU) finalized its decision Wednesday to go on strike against the city's school district, the third-largest in the United States, after protracted labor negotiations did not produce a deal before their deadline.

Earlier in the day, the district canceled classes for Thursday for its 361,000 students.

School buildings will be open for students who need a place to go, officials said. Schools will serve breakfast and lunch, but all after-school activities, including sports, tutoring and field trips, are canceled.

Late Wednesday afternoon, CTU's delegates overwhelmingly reaffirmed their decision earlier this month to go a strike Thursday if the union was unable to come to a contract agreement with Chicago Public Schools (CPS), said teachers union president Jesse Sharkey.

"We have not achieved what we need to bring justice and high-quality schools to the children and teachers of Chicago," he said.

In addition to wage increases, the teachers union is demanding more funding to ease overcrowded classrooms and hire more support staff, two perennial issues plaguing the school district.

District offered 80 changes

The district's bargaining team has offered 80 proposed changes to the current contract related to issues requested by the union, Mayor Lori Lightfoot said earlier Wednesday.

"I was disappointed by the CTU's decision to begin a work stoppage and force the cancellation of classes," Lightfoot said at a late afternoon briefing. "We rolled up our sleeves and negotiated in good faith over a long period of time."

CPS has also offered teachers a 16% raise over five years along with support for oversized classes, enforceable targets for reducing class sizes and adding more support staff across the district, she said.

The mayor said the union's demands would cost the district an additional $2.5 billion annually.

CPS finances "are still recovering from the brink of insolvency, and we do not have unlimited funds," the mayor said.

The district's credit ratings remain at the noninvestment, or "junk" status, although they have improved in the wake of a revised statewide school funding formula that boosted revenue for CPS operations and pension payments.

Thousands of Chicago teachers staged a one-day walkout in 2016 to protest the lack of a contract at that time and failures to stabilize the finances.

Nearly 400,000 students out

District officials encouraged students to go to public libraries and community organizations where educational programs and activities will be offered during the strike.

In addition to schools, park facilities across the city will be open for children during the strike after the city reached a labor agreement Wednesday with the union representing city park workers.

The agreement with the union includes wage increases ranging from 10% to 28% over the 4½ years and for paid vacation to hourly employees based on the number of hours worked, Lightfoot said.