Yes, you can wear leggings on United (but airline can police your clothing).

United Airlines: leggings ban 'not sexist' even though it affects women more, US news

Two girls barred from United flight for wearing leggings: 'Since when does United police women's clothing?

Yes, Airlines Have Dress Codes (and Leggings Are Not Included)

The Yoga Pant Problem Science History Institute

Can You Wear Leggings On United Airlines? – solowomen

I'm an air steward and here's why you should NEVER wear flip flops or Crocs on a plane

Can I Wear Leggings On A Flight To Nyc

United Airlines says customers are 'welcome' to wear leggings — unlike teens who used special passes - Los Angeles Times

Why United Airlines can get away with treating its customers like garbage - Vox

Can You Wear Leggings On An Airplane In Nc International Society of Precision Agriculture

United Airlines: leggings ban 'not sexist' even though it affects women more, US news

A decade of leggings controversy, explained - Vox

Internet Erupts After United Airlines Boots Girls for Wearing Leggings

Should Airlines Have Stricter Dress Codes? We're Diving Into The Debate