No leggings or yoga pants as pants, says United Airlines -- not for its employees or those traveling on employee passes to travel free or discount. The company says that people travelling on its employee travel passes have to dress according to their dress code. General passengers can wear what they like.
The objection is that it is sexist, even though men would technically be turned away too for wearing the same things. The argument is that in actual fact men don't wear that stuff, but women do, so if there is a dress code prohibiting it, then it's sexist. There are also dress code rules for various things men commonly wear, too.
Another argument is that United Airlines is a private company which does not need to respect the freedom of expression of its passengers, and can set appearance guidelines if it wants to. That, of course, would not allow it to enact a rule that discriminates based on sex, though, so if the rule is discriminatory, then it would not be allowed as airlines cannot discriminate based on sex.
Another argument is that airlines should not be policing what people wear, and heck, if they want to wear leggings, then let this guy wear leggings...

I wonder if they'd let that guy sit next to an unaccompanied minor. http://www.clickorlando.com/news/local/ ... anied-kids