CHICAGO — Students are poised to return to Chicago Public Schools after leaders of the teachers union approved a plan with the nation’s third-largest district over COVID-19 safety protocols, ending a bitter standoff that canceled classes for five days.

While school districts nationwide have faced similar concerns amid skyrocketing COVID-19 cases, the labor fight in union-friendly Chicago amplified concerns over remote learning and other pandemic issues.

The deal approved late Monday would have students in class Wednesday and teachers back a day earlier. It still requires approval with a vote of the union’s roughly 25,000 members. Issues on the table have been metrics to close schools amid outbreaks and expanded COVID-19 testing.

Neither side immediately disclosed full details of the proposal Monday evening, but leaders generally said the agreement included metrics to close individual schools and plans to boost district COVID-19 testing. The district notified parents in the largely low-income Black and Latino school district of about 350,000 students that classes would resume Wednesday.

“We know this has been very difficult for students and families,” Mayor Lori Lightfoot said at an evening news conference. “Some will ask who won and who lost. No one wins when our students are out of the place where they can learn the best and where they’re safest.”

In a dueling news conference, union leaders acknowledged it wasn’t a “home run” but teachers wanted to be back in class with students.

“It was not an agreement that had everything, it’s not a perfect agreement, but it’s certainly something we can hold our heads up about, partly because it was so difficult to get,” Union President Jesse Sharkey said.

The Chicago Teachers Union’s house of delegates voted Monday evening to suspend their work action from last week calling for districtwide online learning until a safety plan had been negotiated or the latest COVID-19 surge subsided. The district, which has rejected districtwide remote instruction, responded by locking teachers out of remote teaching systems two days after students returned from winter break.

While there has was some progress on smaller issues like masks, negotiations over the weekend on a safety plan failed to produce a deal and rhetoric about negotiations became increasingly sharp. Some principals canceled class Tuesday preemptively and warned of further closures throughout the week.

Earlier Monday, Union President Jesse Sharkey said the union and district remained “apart on a number of key features, accusing Lightfoot of refusing to compromise on teachers’ main priorities.

“The mayor is being relentless, but she’s being relentlessly stupid, she’s being relentlessly stubborn,” Sharkey said, playing on a reference the former prosecutor mayor made about refusing to “relent” in negotiations. “She’s relentlessly refusing to seek accommodation and we’re trying to find a way to get people back in school.”

Lightfoot accused teachers of “abandoning” students and shot back at the union president.

“If I had a dollar for every time some privileged, clouted white guy called me stupid, I’d be a bazillionaire,” Lightfoot, who is Black, told WLS-TV.

By evening, she had said she was optimistic with the latest proposal, which went to union leaders for a vote.

Her first term in office has been marked by other battles with the influential union, which supported her opponent in the 2019 election, including a safety protocol fight last year and a 2019 teachers strike.

Developments in the fight, with pending complaints before a state labor board, made international headlines and attracted attention from the White House. Press secretary Jen Psaki said Monday that President Joe Biden, who has pressed for schools to stay open, had remained in touch with Lightfoot and Illinois Gov. J.B. Pritzker during negotiations.

Parents and advocacy groups also stepped up calls Monday for quicker action.

A group of parents on the city’s West Side — near the intersection of largely Black and Latino neighborhoods — demanded students return immediately.

Cheri Warner, the mother of 15-year-old twins, said the sudden loss of in-person learning has taken a toll on her family.

One of her daughters has depression and anxiety, and winter is always difficult. Losing touch with her friends and teachers adds to that burden, Warner said.

The girls “missed their whole eighth grade year and it felt like they weren’t really prepared for high school,” Warner said. “They’re all trying to figure out how to catch up and it’s a really stressful situation.”

Other parents said the district needs to do more.

Angela Spencer, an organizer with the Kenwood Oakland Community Organization and a nurse, said she’s concerned about her two kids’ safety in schools. Spencer said her kids’ schools weren’t adequately cleaned before the pandemic and she has “no confidence” in the district’s protocols now.

Several families represented by the conservative Liberty Justice Center in Chicago, filed a lawsuit in Cook County over the closures, while more than 5,000 others signed a petition urging a return to in-person instruction.

District officials, who call the union action “an illegal stoppage” had kept buildings open for student meal pickup and said that schools with enough staff were allowed to open their doors to students. Some teachers showed up despite union directives; district officials estimated about 16% of teachers did so Monday.

Three schools, including Mount Greenwood Elementary, were able to offer instruction Monday, according to district officials. Parents at the largely white school on the city’s southwest side expressed relief.

City officials argued that schools are safe with protocols in place. School leaders have touted a $100 million safety plan, including air purifiers in each classroom. Roughly 91% of staff are vaccinated and masks are required indoors.

Union officials have argued the safety measures fall short and the district has botched testing and a database tracking infections.

There were small signs of agreement in recent days.

The district has purchased KN95 masks for students and teachers, agreed to bring back daily COVID-19 screening questions for anyone entering schools, and added more incentives for substitute teachers.