Union members voted Sunday to work remotely starting on Wednesday.
CPS plans to return to in-person classes for high schoolers next Monday.
But the union says full time in-person classes aren't safe and there should be a hybrid system.
"We're very concerned about schedule in our schools," said CTU President Jesse Sharkey. "You've got some very large schools which are bringing all of our students, all the students who have opted in back in every day."
"There's a question about having safe space for faculty and staff to work. And those underline two other issues which you heard a lot of presentation about. About the question of whether or not our most medically-vulnerable people can have accomodations," Sharkey said. "And then finally the question about the increase in positivity rate, increase in transmission, especially among young people and us wanting to secure a commitment from the schools, but really from the mayor and from the city about our commitment to try to vaccinate young people."
A number of large, suburban high school districts returned to in-person learning last week.