(WASHINGTON) — The Education Department on Monday launched civil rights investigations into five states that have barred indoor masking mandates, alleging that the governors are creating an unsafe learning environment for students with disabilities at heightened risk of severe illness from COVID-19.

It’s an aggressive new legal tack from the Biden administration to challenge Republican governors who insist indoor mask mandates don’t work.

The Centers for Disease Control and Prevention has found that schools are generally safe if students and staff universally wear masks. School districts who struggled with COVID-19 outbreaks this year – oftentimes sending thousands of kids home – typically did not require masks.

The investigations focus on Iowa, Oklahoma, South Carolina, Tennessee, and Utah. The Education Department says it is not including Florida, Texas, Arkansas and Arizona at this time “because those states’ bans on universal indoor masking are not currently being enforced as a result of court orders or other state actions.”

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