Teachers at the school attended by a 17-year-old who died of COVID-19 last week called out in large numbers Monday, forcing Olney Charter High School to go virtual — and the company that runs the school has threatened legal action, the teachers union says.

Alayna Thach, a senior at Olney, died Dec. 13. Teachers at the school have asked ASPIRA of Pennsylvania for stepped-up health and safety protocols; the company says it has made changes, but teachers contend more are needed.

In total, 41 staff members were absent Monday, ASPIRA officials said, which includes a handful of staff in quarantine for COVID-19 exposures. That represents about a third of Olney’s unionized staff; the school educates 1,800 students.

Principal James Thompson said at a news conference that ASPIRA was “working with legal counsel” to determine next steps, and that classes would be conducted virtually through Thursday, the last day before winter break. Students will also attend class virtually for a week in January, immediately after break concludes.

The staff callout made it “not feasible for us to do anything other than what we did to maintain the safety and security of our students,” Thompson said.

» READ MORE: An Olney Charter HS student died of COVID-19. Teachers say the school needs better health safeguards.

ASPIRA said it believed teachers were in violation of their collective bargaining agreement. Most charter schools’ faculty are not unionized; Olney’s organized and ratified their first contract in 2017.

Thompson, who remembered Thach as a “fantastic young lady,” said he believed the union was using her death “to possibly further an agenda. Unfortunately, I don’t think this was the time or the way to go about this.”

Arthur Steinberg, president of the American Federation of Teachers Pennsylvania, to which the Alliance of Charter School Employees at Olney Charter belongs, blasted what he called ASPIRA’s “dishonest reaction” and “depraved priorities,” saying the organization was more concerned with public image than with safety.

“When many students are already learning virtually due to quarantine, it is disingenuous to place blame on our dedicated educators who demand and deserve a safe teaching environment for them and their students,” Steinberg said in a statement. “The union hopes that teaching remains virtual only as long as it takes to slow the spread of the virus and perform quick and thorough contact tracing.”

Sarah Kenney, an Olney history teacher and vice president of the teachers union, said Thach’s death should have been a “wake-up call” for ASPIRA.

“Our union unequivocally did not organize what management are labeling a ‘mass callout,’” Kenney said. “However, in the aftermath of a student death, dozens of students learning virtually due to quarantine, and the surging delta and omicron variants, Olney’s management should have been more proactive in moving to fully virtual learning before late last night.”

In a letter to families, Thompson said the Olney Charter administration condemns any action by employees in violation of their contract, “especially this action which disrupts Olney’s ability to provide in-person education to our students and the lives of their families who now must make alternative plans for their children.”

ASPIRA officials said students’ education was not disrupted, despite the callouts, and said counselors will remain available to those struggling with the death of Thach, a beloved classmate known for her kindness and intelligence. Teachers who did not report to work left assignments students could complete on their computers. Those who did come into the building conducted live lessons via Zoom.

At a memorial service for Thach held outside the school Friday afternoon, teachers expressed serious concerns about conditions ranging from a lack of mask compliance and social distancing to no asymptomatic testing for staff. Thach’s family said she was concerned about safety at the school, too, and was trying to start a petition to allow students to eat lunch outside.

Teachers said they began raising their objections when school began, but little has been done. The death of Thach, who was unvaccinated but had plans to get the shot in January, as well as a rise in cases, was an impetus for the increased action, teachers have said.

» READ MORE: Alayna Thach’s family speaks about COVID-19 death of 17-year-old: ‘How is this possible?’

ASPIRA has said it plans to begin asymptomatic staff testing in January. Ten percent of students whose parents consent to testing receive COVID-19 tests currently, but staff say so few parents have signed consent forms that the testing is not meaningful.

“Olney has implemented several preventative measures that are not used by other local schools because of again its goal to provide the safest school environment possible during the pandemic,” Thompson said in the note to families.

Kathryn McKinley, Olney’s director of special education and specialized services, said the school was “honestly very proud of the proactive steps that we’ve taken in this situation.”