Yes, you can wear leggings on United (but airline can police your clothing).
Airplane Leggings - Etsy
Womens Leggings w/Airplane Design - Shop All Apparel | One Plane Jane
Two girls barred from United flight for wearing leggings - The Washington Post
What NOT To Wear On A Plane VS. What You Should | Ways of Style
Airplane Leggings for Sale | Redbubble
After Barring Girls for Leggings, United Airlines Defends Decision - The New York Times
Woman left mortified after being kicked off plane over 'inappropriate' leggings - World News - Mirror Online
Leggings on a plane? Not so horrifying, say etiquette experts
Airplane Leggings - Etsy
Here's the Reason a Group of Girls Wearing Leggings Weren't Allowed to Board a United Airlines Flight | Glamour
Plane expert warns you should never wear leggings on a flight
The Comfiest Airplane Pants for Travel
Womens Leggings - Lets Go Airplane - Shop Apparel | One Plane Jane
What NOT To Wear On A Plane VS. What You Should | Ways of Style
Leggings on a plane? Not so horrifying, say etiquette experts
