The U.S. government’s mask mandate for people on planes, trains, ferries and other modes of public transportation has been challenged in a lawsuit filed by 21 states on Tuesday.

The CDC’s mask mandate took effect on Feb. 1, 2021 and was recently extended until April 18, although the agency has said it is considering easing the rules and taking a more targeted approach. Right now, the mandate requires “the wearing of masks by people on public transportation conveyances or on the premises of transportation hubs,” according to the CDC. Other states involved in the lawsuit are: Alabama, Alaska, Arizona, Arkansas, Georgia, Idaho, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, Ohio, Oklahoma, South Carolina, Utah, Virginia and West Virginia.

The 21 states are not the only ones who want the mask mandate for public transportation lifted. Last week, the chief executives of the country’s largest airlines asked the president to let federal mask mandates at airports and on planes lapse on April 18, along with COVID-19 testing requirements for international travelers. The American Public Health Association is supportive of the airline’s request.