Teachers from a few dozen campuses across the Houston Independent School District staged a “sick-out” protest Thursday, calling out of work to demand a safer learning environment for themselves and their students during the pandemic.

Among their demands: capping class sizes at 15 students with six feet of social distancing required; serving meals outside or in large, well-ventilated areas, and not in the classroom as many schools are doing; improving HVAC and air circulation for all classrooms; and adding mask policies to the student and staff code of conduct.

The planned sick-out in Houston comes at the same time HISD is reopening 16 schools that had to close this week because of confirmed or presumed cases of COVID-19 on campus. In a statement late Wednesday, HISD said that all of its 280 schools will reopen for face-to-face instruction Thursday, and that schools that had temporarily closed have been deep-cleaned and disinfected.

HISD also announced that it’s decided to revise its policy on when a campus should close due to COVID-19. Citing a review of procedures in collaboration with the Houston Health Department, HISD will now close schools and shift their students to virtual learning if there are two or more confirmed cases of COVID-19.

Previously, the state’s largest school district had stricter criteria: Just one confirmed or presumed case of COVID could trigger a school’s closure for deep-cleaning. That led to the 16 schools closing after the first day of in-person learning this week.

Teachers in Houston and across the state are concerned about the risks to their health and students as campuses reopen for face-to-face instruction during the pandemic. In Austin, students planned a “sick out” to protest reopening policies and support their educators.

In Texas, it’s illegal for public school employees to strike. If they do, they can lose their teaching certificates and their pension benefits with the Teacher Retirement System permanently revoked.