The Union had to send out a reminder:

This is actually the policy for every game and it’s been this way for as long as anyone can remember. You’re not allowed to wear opposing team colors in The River End, where the Sons of Ben and Keystone State Ultras sit. No Miami jerseys, no Argentina Messi jerseys, no PSG, Barcelona, Newell’s Old Boys, nothing besides Philadelphia Union colors.

The policy is perfectly fine. Most teams have something like this in place. I suppose they had to send a reminder on Twitter because some supporters cashed out and sold their tickets, or couldn’t make a Tuesday night, or just wanted to avoid the Messi shit show (I talked to a guy who got $400 and took the money because he didn’t wanna deal with Messi fanboys). In this case, if you show up to TRE wearing Messi gear, you get relocated to standing room only. I would relocate ’em to the bagster, personally.