Chicago Public Schools (CPS) canceled classes on Wednesday and are accused of restricting access to teacher portals after the teachers’ union voted in favor of remote learning amid a rise in cases of COVID-19 powered by the Omicron variant.

The nation’s third-largest school district rejected a return to remote learning, but the Chicago Teachers Union (CTU) voted Tuesday to return to online learning with 73% approval. After canceling lessons, the CPS is now accused of excluding teachers from the school’s online learning system.

“We are being inundated with calls and emails this morning from educators who have attempted to log into their platforms to connect with their students and teach remotely and safely, but are being blocked by Mayor Lightfoot,” said CTU on Twitter.

Many teachers are posting their frustrations online with the hashtag #LoriLockout, in reference to Chicago Mayor Lori Lightfoot and her previous disputes with the union.

“Half the middle school is in quarantine. More than half of my 5th graders are sick,” one teacher wrote on Twitter. “I voted to work remotely because my school is unsafe. I want to teach today, but CPS blocked me. [The CTU] We didn’t call a strike or a work stoppage, we called for security.”

“Ready to teach, provide specialized instruction to diverse learners, write IEPs, and communicate with families,” another teacher said, “but [Lightfoot, Chicago Public Schools chief executive officer Pedro Martinez, and CPS] locked me up. They are responsible for my students not receiving their legally authorized services today.”

District officials have called the union’s action an “illegal work stoppage,” but teachers say they fear for the safety of their students and themselves with rising COVID cases.

“We would rather be in our classrooms teaching, we would rather have the schools open,” CTU President Jesse Sharkey said at a press conference Wednesday. “What we’re saying though is that right now we’re in the middle of a major surge, it’s breaking all records and the hospitals are full. What if we don’t get okay, it’s that the thrust is going down, and when the surge goes down, we’ll be back in the classrooms.”

Newsweek has contacted CTU for comment.

Union members were ordered to try to log into education systems on Wednesday, even though the district said there would be no instruction and did not distribute devices to students until after union votes, which were announced just before 11 p.m. Tuesday.

District officials blamed the union for the late cancellation, saying that despite safety measures, including high teacher vaccination rates, “our teachers are unwilling to report to work.”

“We are deeply concerned about this decision but even more concerned about its impact on the health, safety and well-being of our students and families,” the district said in a statement.

District leaders said a plan to “continue student learning” would arrive later Wednesday. School officials said teachers who fail to report to schools on Wednesday will not be compensated. Last year, in a similar debate, the district punished teachers for not coming to schools.

Keyonna Payton, a teacher at Park Manor Elementary School who also chairs its safety committee, said she was teaching remotely Monday and Tuesday because most of her students were home in quarantine.

Payton said she was vaccinated and boosted, and had a child attending school in the district who was also vaccinated, but she feared the variant could spread to her family.

“I am doing my part to try to protect my children. However, I am afraid of this virus and its variant because of how quickly it moves and spreads,” she said during a Wednesday press conference. “I’m scared because I have a husband, I have a young child and I have a 91-year-old grandmother with underlying health issues.”

Contentious issues in the district include actions that would trigger school closures. The district offered guidelines for individual school closures, saying safety measures such as mandatory masks, availability of vaccines and improved ventilation make schools one of the safest places for children. But the union has proposed measures for the district-wide shutdown, citing risks to students and teachers.

A fierce battle took place last January over similar issues, causing a bumpy start to the district’s return to in-person teaching after its first remote use in March 2020.

Schools CEO Pedro Martinez said the buildings would remain open for administrators, staff and “essential services,” but not for the instruction of students in the district that is largely low-income and black and Latino. District officials said schools would provide food service from 9 a.m. to 12 p.m. and COVID-19 testing would continue as planned, but after-school activities would be canceled. The district also provided a list of sites in the city with available daycare.

In response to union concerns, the district said it had provided 200,000 KN95 masks to teachers, would enable schools to bring back daily health screening questions for students and building visitors that were needed year round. last school year, and would specify the parameters for closing individual schools. For example, the district said it would transition to remote learning in an elementary school if 50% of its classrooms had more than 50% of its students instructed to self-isolate or quarantine.

The union, which has around 25,000 members, had sought the same measures to close schools from an agreement last year, which expired before the start of the new school year. That includes a two-week district-wide pause on in-person learning if the citywide COVID-19 test positivity rate increases for seven consecutive days, for example.

Union leaders said more safety protocols were needed and the COVID-19 surge was causing staff shortages. The district said about 82% of its roughly 21,600 teachers showed up for work Monday, which was lower than normal, but classes were covered by substitute teachers and other staff.

District officials said student attendance for the week was not yet available.

About 100,000 students and 91% of its more than 47,000 employees in the district are vaccinated, according to the district.

The Associated Press contributed to this report.