School support staff have ended their strike, Chicago Public Schools chief Janice Jackson said Sunday evening, after reaching a tentative agreement on a new contract. But classes will remain cancelled Monday because of the continuing strike by teachers — their longest walkout in more than three decades.

The 7,500 members of SEIU Local 73 — including bus aides, custodians, classroom assistants, and security officers — had walked out Oct. 17. The union was fighting for pay increases, improved benefits like a paid Christmas break, better definition of duties of special education classroom assistants, and an end to outside management of custodians by Sodexo and Aramark.

Jackson joined the district’s negotiations with teachers Sunday afternoon, the Chicago Teachers Union announced.

Jackson is credited with helping avert a long teachers walkout in 2016, when as the district’s No. 2 administrator she joined the bargaining table at the last minute.

On Sunday, daylong talks with the teachers union failed to bridge differences, and the district  announced in the afternoon that it would not offer classes nor after-school activities on Monday.

“As of 4 p.m., CTU leadership has informed us that there is no possibility of a deal today,” the district tweeted.

At a press briefing Sunday night, Mayor Lori Lightfoot struck a stern tone as she defended an offer that she said “leads with equity” in the face of serious financial constraints and that addresses issues the union has identified as priorities, including class size and staffing.

“This is by any estimation an incredible offer,” Lightfoot said. “And despite all of this, the CTU has not accepted it. We are enormously disappointed that CTU simply cannot take yes for an answer.” 

Lightfoot said that the city would release details of the tentative SEIU Local 73 contract after union members ratify the it. According to one union member who was briefed on a conference call, the deal includes a 16% raise over five years, as the city has originally offered. Bus aides, security, custodians and special education aides will get additional raises when they complete certain years of services.

The deal also makes some improvement in working conditions sought by the union, the SEIU members said. Among them, bus aides will have the opportunity to work at schools in between working their routes, meaning they can get paid in the middle of day when they’re currently forced to be idle.

The five-year proposed SEIU contract would be retroactive to last year, and will expire in 2023 — a period that Mayor Lori Lightfoot had sought.

On Sunday morning, the distance between the two sides was huge, the district’s Chief Education Officer LaTanya McDade said.  While the district and union agreed on what schools should offer students, she said, they differed on how to be able to do that — and how much to spend.

Chief Operating Officer Arne Rivera said the gap between what is already on the table and what the union is asking for is about $100 million. It would not be responsible for the city to approve spending that much, he said.

The union estimated the gap at $38 million a year.

When pressed on Thursday about when in the negotiations she would consider stepping in to the talks, Lightfoot hedged. “I will go when I think it’s appropriate for me to add value,” she said. “You may not have noticed, but I have a lot of things on my plate.”

Meanwhile, students plan to protest at City Hall on Monday, the eighth day of the strike.