The U.S. Department of Education sent a warning to five states on Monday that their statewide bans on mask mandates, including in schools, could violate students’ civil rights.

Suzanne B. Goldberg, the department’s acting assistant secretary for civil rights, sent letters to state education leaders in Iowa, Oklahoma, South Carolina, Tennessee, and Utah, informing them that the department’s Office for Civil Rights is investigating whether their bans are discriminatory.

At the center of the department’s concerns, according to Monday’s letters, are students with disabilities who may be at heightened risk for severe illness from COVID-19. Goldberg’s letters say these investigations will focus on whether the state bans are discriminatory by preventing students with disabilities from safely returning to in-person education.

Federal law “guarantees qualified students with disabilities the right to a free appropriate public education in elementary and secondary school,” Goldberg wrote in each of the letters. “This includes the right of students with disabilities to receive their education in the regular educational environment, alongside their peers without disabilities, to the maximum extent appropriate to their needs.”

If students with disabilities do not feel safe returning to school because their classmates cannot be required to wear masks, the department’s argument goes, then these bans could be considered discriminatory and violate either Section 504 of the Rehabilitation Act of 1973 and/or Title II of the Americans with Disabilities Act of 1990.

The announcement comes after President Biden issued a memorandum on Aug. 18, in which he directed Secretary of Education Miguel Cardona to ensure that “governors and other officials are giving students the opportunity to participate and remain in safe full-time, in-person learning without compromising their health or the health of their families or communities.”

If the Education Department ultimately finds that these mask mandate bans do run afoul of federal civil rights law, it could threaten to withhold federal funding, though, on a recent appearance on NBC’s Meet the Press, Cardona conceded that was less than ideal.

“When we talk about withholding funds, those who suffer are the students,” Cardona said. “Withholding funds doesn’t usually work. If anything, it adds insult to injury to these students who are trying to get into the classroom.”

The department says it is not now investigating other states with similar bans — including Texas, Florida, Arkansas and Arizona — because those bans are not currently being enforced, either due to court orders or other actions.