CHICAGO (CBS) — With a teachers’ strike all but guaranteed, Chicago Public Schools has canceled classes on Thursday, as Mayor Lori Lightfoot said “CTU hasn’t gotten the message” that the city can’t meet all of its contract demands.

Barring an unexpected breakthrough sometime Wednesday, the Chicago Teachers Union bargaining team has recommended a strike starting Thursday, and Mayor Lori Lightfoot said classes will be cancelled, but stressed there is a contingency plan in place to keep school buildings open so students have a safe place to go.

Wednesday morning, Lightfoot made it clear the city is expecting a strike to begin on Thursday, regardless of what happens in negotiations Wednesday morning.

Calling the offer the city has made to the teachers the best in the union’s history, Lightfoot said “at every turn, we’ve bent over backwards to meet the union’s needs.”

“Despite all of this, the Chicago Teachers Union intends to forge ahead with a strike,” the mayor said Wednesday morning at City Hall.

Lightfoot said, as the daughter of a union steelworker, she supports the right to strike when necessary, but she believes it’s not appropriate for teachers to walk out when the Chicago Public Schools and CTU are making “concerted progress” on an agreement.

“The union has told the public repeatedly that the two issues we need to resolve are class size and staffing, and we have met their needs, but behind the scenes they’ve continued to bring up additional bargaining issues that they say must be resolved before they can have a contract,” she said.

The mayor said, for example, the union has proposed more teacher prep time, which would reduce the amount of instructional time for students by 30 minutes in the  morning.

“We won’t do that. We will not cheat our children out of instruction time, and I won’t agree to any changes that do that,” Lightfoot said.

Lightftoot also said, in addition to the union’s demands on class sizes and staffing for nurses, social workers, case managers, and librarians; CTU is sticking with demands it has made since January that would add $2.5 billion in costs to its contract, nearly doubling its size.

“CTU hasn’t gotten the message,” the mayor said. “Agreeing to an extra $2.5 billion a year in costs would be completely irresponsible at any time, but especially in the economic times that we face now.”

In addition to the 25,000 teachers at CPS, approximately 7,500 school support staff and 2,500 Chicago Park District workers represented by SEIU have set a Thursday strike deadline to coincide with the teachers’ work stoppage.

CPS Chief Executive Officer Janice Jackson said, with a teachers’ strike all but guaranteed to begin Thursday morning, all classes and after-school activities will be cancelled. Schools will remain open, staffed by non-union CPS employees. She also said public libraries and some park facilities will be open to students.

Meanwhile some private agencies also are getting ready for an influx of students if teachers walk out.

It will come down to a teachers’ union vote planned for Wednesday afternoon.

In the meantime, organizations like the Neighborhood Boys and Girls Club plan to open early Thursday if teachers walk out.

“We will be open,” said Bonnie Werstein, director of operations for the club. “We will be available for every day of the strike.”

Werstein said the organization could see between 100 and 200 students if teachers do walk out.

“We do have teachers’ children coming, administration children coming and also our after school children and community children. They are going to have open play here in our game room and do board games or ping pong. They are going to play in the gym.”

There is a price though — $60 a day.

But the fee can be waived for families who are part of federal or state programs.

“We need to take care of the children that are most vulnerable and support the families that need us,” said Werstein.

The organization has been here before. In 2012, the last time teachers went on strike, this is where many parents brought their children. It’s a service that’s especially vital for parents who don’t have other  options.

“They don’t have families that are local,” Werstein said. “They are immigrant families, so their support system is very small, and we’ve become that support system for them. We’ve become their family.”

The Salvation Army also has three locations that will open early and take in Chicago Public Schools students. Two of those locations are free of charge.