Nine flight attendants from six different airlines have filed a lawsuit against the U.S. Centers for Disease Control and Prevention and the Department of Health and Human Services over the federal mask mandate on air travel, claiming the measure is unconstitutional, ineffective, and harmful to their health and safety.

In the lawsuit, filed March 24 in the U.S. District Court for the District of Colorado, the flight attendants claimed the measure obstructs breathing over many hours and causes a litany of other health problems. Enforcement of the mandate also puts attendants in danger of retaliation from unruly passengers who refuse to comply, they added.