Chicago(CNN) With still no agreement between school system administrators and teachers, some 340,000 students will miss class again Thursday, the Chicago Public Schools CEO said.
"Right now, as I'm looking at what is happening with our staff, where they are being discouraged from coming to our buildings, we have no choice but to cancel classes tomorrow," CEO Pedro Martinez said at a news conference Wednesday.
A letter sent to the students' families says, "Caregivers should not plan to send their children to school."
Mayor Lori Lightfoot pleaded with teachers to return to the classroom.
"If you care about our students, if you care about their families, as we do, we will not relent, enough is enough! We are standing firm and we are going to fight to get our kids back in in-person learning! Period. Period! Full stop!" Lightfoot said.
Martinez said negotiations with the Chicago Teachers Union will continue.
"We had another negotiation today. We're not going to stop," he said. "We still believe that the right approach is not a district-wide hammer that does a brush across the entire school system calling the schools unsafe which there's no evidence to show that."
One union official with knowledge of ongoing negotiations told CNN that it was a productive day and that there was "movement."
Earlier Wednesday, the president of the Chicago Teachers Union said students might be out of school for two weeks if the two sides can't reach a resolution on Covid-19 safety measures.
The showdown in the nation's third-largest school district exemplifies debates playing out across the country: When and how should students return to classrooms during the Omicron variant surge?
A day after in-person learning resumed Monday, the union voted Tuesday night to teach virtually instead.
The school district responded by canceling school for Wednesday, insisting students need to return to classrooms.
The union said conditions for in-person learning were unsafe, citing inadequate staffing and testing as new Covid-19 cases and new hospitalizations among children reached record highs.
"I'm afraid because I have a husband. I have a young child. I have a 90-year-old grandmother with underlying health conditions and issues," educator Keyonna Payton said Wednesday.
"So, I would just appreciate being able to work in an environment where at least the students are all PCR-tested weekly, and we have their results to go to in-person instruction."
If the stalemate continues, teachers might not return to classrooms until January 18, union President Jesse Sharkey said Wednesday.
He said teachers might return to schools earlier if the current Covid-19 surge subsides or if the union reaches an agreement with the city and school district officials.
The school district's letter to parents said "many staff members, including many teachers," went to their schools on Wednesday.
"Some schools have enough staff reporting to work to return to in-person instruction as soon as Friday," the letter says.
Schools will continue to provide take-home breakfasts and lunches and the city is offering several child care options, according to the letter.
Chicago Public Schools described the union's vote to teach remotely as an "unfortunate decision."
Teachers will not be paid for refusing to report to school in person, Martinez said Tuesday. City officials said the union decision amounted to an illegal work stoppage.
Lightfoot said going remote would "harm hundreds of thousands of Chicago families who rely upon CPS for the daily needs for their education, for their nutrition, for their safety. That's real harm."
Chicago Health Department Commissioner Allison Arwady said families should not be overly concerned about the virus.
"Especially if you're vaccinated, your child is vaccinated, this is behaving really like the flu. And we don't close school districts, especially for extended periods of time, for the flu," Arwady said Tuesday.
"I remain extremely comfortable with children continuing in-person education."
Martinez said keeping students in schools can actually help the district better access families to get them tested and vaccinated.
"One of the reasons why I continue to plead, including with CTU leadership, to keep the schools open and to keep classes going (is) because that's our best chance to reach families," he said.
Even though school was canceled for Wednesday, some educators tried to log on to their remote teaching platforms -- only to discover they were locked out, the Chicago Teachers Union tweeted.
Chicago Public Schools officials didn't confirm whether they had locked teachers out of their remote platforms. But Wednesday morning, the school district reiterated to CNN that the union's vote amounted to "a work stoppage."
Payton said the lockout was "disheartening and disappointing" because it wasted a day when students could have been learning.
"So instead of trying to develop a plan to ensure that students could learn today, the schools were closed," the educator said. "So they had no instruction."
Sharkey said teachers would rather be in classrooms -- but in-person learning without added safety precautions would put teachers, staff, students and their families at risk.
"This is a virus that's raging through the city," the union president told reporters.
He said the city of Chicago has "failed to deliver a whole number of basic demands that we need in the schools, has failed to provide adequate staffing, adequate cleaning in the schools, has failed to provide adequate testing, has failed to address our concerns as people going to the schools."
As a result, Sharkey said, "teachers and the school staff have decided the only thing we get to control is whether we go into the buildings."
Carolina Barrera Tobón has a first grader and a third grader in Chicago Public Schools. She said she's frustrated with the teachers' union as well as the school district and mayor.
"I am very disappointed in the Chicago Teachers Union for the fearmongering tactics and negative rhetoric regarding this vote. I am equally disappointed in the CPS CEO and our mayor," said Tobón, a professor at DePaul University.
"CPS has dropped the ball on so many important decisions and the implementation of safety procedures. And I honestly do not trust the teachers union to stay remote for only two weeks after their continued spread of misinformation regarding the safety of our schools."
Others worried about the negative effect of distance learning on the children.
"Here we go again," said Natasha Dunn, mother to a seventh grader at Harriet Tubman Elementary School.
"I am completely against schools closing. Jill has been in school pretty much every day since August without any issues," Dunn said.
"She was so excited to be back in school -- interacting with her classmates, joining clubs and participating in sports," Dunn said. "We have started seeing her grades improve and her overall mood. Closing the entire district down will only interrupt her progress."