The announcement by the American Federation of Teachers, which boasts roughly 1.7 million members, comes about a month before school districts across the U.S. are scheduled to resume classes. Various districts have come up with differing plans to prevent coronavirus spread, with New York City opting for hybrid in-person and at-home learning while Los Angeles schools will begin the school year entirely by distance learning.

“Just as we have done with our healthcare workers, we will fight on all fronts for the safety of our students and their educators,” AFT president Randi Weingarten said in an online conference. “But if the authorities don’t get it right, and they don’t protect the safety and health of those we represent and those we serve, nothing is off the table—not advocacy or protests, negotiations, grievances or lawsuits, or, if necessary as a last resort, safety strikes.”

Weingarten has repeatedly criticized President Trump’s handling of the pandemic, including his push to reopen schools in the fall. Reopening schools remains a difficult undertaking because of a lack of data in the U.S. on coronavirus among children.

“Of all the age categories, we have the least evidence of testing and results in children,” Dr. Deborah Birx, coordinator of the White House Coronavirus Task Force, told an Ohio ABC affiliate on Tuesday. However, “I think schools, through the CDC guidelines, will be able to see how to do social distancing, how to do handwashing, how to mask young children and how to protect each other and, more critically, how to protect both the teachers and the vulnerable children.”

YMCA childcare centers in New York have succeeded in taking care of about 40,000 children throughout the city’s lockdown, with relatively few outbreaks of coronavirus.