The Chicago school district and teachers union are disagreeing on the safety conditions of schools amid the spread of the omicron variant.

The Chicago Teachers Union (CTU) on Tuesday voted in favor of returning to remote learning until the recent COVID-19 case surge "substantially subsides" or until Mayor Lori Lightfoot "signs an agreement establishing conditions for return that are voted on and approved by the CTU House of Delegates." 

Chicago Public Schools (CPS) said Tuesday it would cancel classes Wednesday in response to the vote as the mayor and school district go head-to-head with the union, which held a press conference on Wednesday morning to answer questions from reporters and the public. 

CHICAGO TEACHERS UNION VOTES TO RETURN TO REMOTE LEARNING DUE TO COVID-19 SURGE

"Our mayor and her doctor spent a lot of time yesterday talking about how COVID impacts young people. They're not speaking specifically to the issue of how COVID is impacting staffing," CTU Vice President Stacy Davis Gates said during the meeting. "…We don't have enough grownups in the building, so instruction isn't happening. We are warehousing children in large spaces with warm bodies."

CPS told Fox News that 82% of staff showed up to work on Monday after a two-week holiday break. Public schools will only close if 40% of staff calls out sick. Additionally, 90% of CPS staff is vaccinated, according to the district.

Pre-kindergarten teacher Sarah McCarthy works with a student at Dawes Elementary in Chicago on Jan. 11, 2021. (Ashlee Rezin Garcia/Chicago Sun-Times via AP, Pool, File)

Pre-kindergarten teacher Sarah McCarthy works with a student at Dawes Elementary in Chicago on Jan. 11, 2021. (Ashlee Rezin Garcia/Chicago Sun-Times via AP, Pool, File)

The union also criticized CPS for 25,000 COVID-19 tests that were deemed "invalid" after the tests piled up at FedEx drop boxes. The tests must be processed within 48 hours to be accurate, but the testing vendor, COLOR, told parents that the tests were delayed because of "weather and holiday-related shipping issues." The vendor told CBS Chicago it’s supporting extended testing dropoff hours and more testing this week. 

CPS also said it tested 10,000 students Monday of the school district's 340,000 total students.

25K CHICAGO PUBLIC SCHOOL COVID TESTS RENDERED ‘INVALID’ AS SHIPPING ISSUES MOUNT

Chicago's COVID-19 cases have spiked to record highs with a daily average of 4,775 cases, or 176.4 per 100,000 residents, but deaths remain low with a daily average of 11 deaths, or 0.4 per 100,000 residents. Nearly 65% of all Chicagoans are fully vaccinated.

"I'm very appreciative of well over 80% of our staff that came in, greeted our children – all of the students that came in, even with pressure that families were feeling to keep their children home with … continued misinformation about schools not being safe. There is just no evidence of that," CPS CEO Pedro Martinez said Tuesday, adding that closures should happen on a school-by-school basis rather than a district-wide basis.

Chicago Teachers Union members display signs ahead of a car caravan where teachers and supporters demanded a safe and equitable return to in-person learning in Chicago, Illinois, on Dec. 12, 2020.

Chicago Teachers Union members display signs ahead of a car caravan where teachers and supporters demanded a safe and equitable return to in-person learning in Chicago, Illinois, on Dec. 12, 2020. (Max Herman/NurPhoto via Getty Images)

He continued: "You can literally go to our website and go look at classroom by classroom – we have indicators that tell us if we have filtration issues in any given classroom. All of our children are wearing masks. We social distance where possible. There's regular washing of hands. And we address issues at the school level."

Parents can "work with" individual schools if they do not want their children to return to in-person classes, he added.

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Lightfoot said "hundreds of thousands" of families rely on CPS for their "daily needs," including education, food and safety for children. Chicago Public Health Commissioner Dr. Allison Arwady said every Chicago public school building will have access to COVID tests. She also noted that no children have died of COVID-19 since October, even as omicron cases surge in the city.

The teachers union disagrees that conditions are safe enough to teach in-person.

Lori Lightfoot speaks during a Jan. 4 press conference (Facebook/ Chicago Public Schools)

Mayor Lori Lightfoot speaks during a Jan. 4 press conference. (Facebook/ Chicago Public Schools)

"We want to be in our buildings educating our students – but we have a right to rigorous layered mitigation that ensures that we’re also not sacrificing our lives for our livelihoods," CTU President Jesse Sharkey said in a Dec. 30 statement. "CPS has the funds – over 2 billion by their own count – to be able to do what’s necessary starting Monday morning to keep people safe. If those mitigations aren’t in place by Monday to protect our educators, students and families, we predict chaos."

Meanwhile, President Biden, American Federation of Teachers President Randi Weingarten and national health organization such as the American Academy of Pediatrics are pushing to keep schools open after winter break.

"Let’s be clear here regarding Chicago schools – No one wants schools closed," Weingarten tweeted Wednesday. "…We do that through working together to roll out testing, masking, and vaccination – and most major districts have done it. NYC and LA have instituted rigorous testing programs to catch asymptomatic COVID spread in its tracks & keep educators, students, and their communities safe. Mayor Lightfoot should be moving heaven and earth to get it right in Chicago."

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U.S. Surgeon General Vivek Murthy and the American Academy of Pediatrics have noted that school closures disproportionately impact minority students in urban school settings who may not have access to the same remote-learning tools as children in suburban areas.

A January 2021 report from Centers for Disease Control and Prevention (CDC) researchers published in the Journal of the American Medical Association (JAMA) noted that as schools reopened for in-person instruction, "school-related cases of COVID-19 have been reported, but there has been little evidence that schools have contributed meaningfully to increased community transmission."

Fox News' Ronn Blitzer, Emma Colton and Brie Stimson contributed to this report.