A favor.

[Caradoc]

It's my mom that has an issue with it. My uncle said it is to be a formal occasion and left it at that.

I'd leave it up to the bride and groom, and the bounds of good taste.

Do you have the kit to go "formal?" If not, don't wear the kilt.

If you show up to a "formal" gathering (even in the United States) wearing a Utilikilt, T-shirt, and nylon sporran, you'll look like a buffoon.

If you've got a nice set of black leathers, a decent Argyll, Crail, or Prince Charlie coat (with or without the waistcoat), and all of the accoutrements to pull it off, take a picture of yourself in the outfit and send it to the bride and groom, and if they *want* you there in that outfit, so be it. If you don't have the kit to do it, please don't try it. See these threads for ideas:

"Dressy"

"Formal"

The latter would be where you should aim if the guests are supposed to be in tuxedoes, while the "Dressy" might be passable if they're in the equivalent of weekday business suits.

I know my mother wouldn't argue the wishes of a bride and groom that weren't her children - would yours?

Keep this foremost in your mind, though - it's their day, not yours, and I (and my grandmothers, living and dead) would highly disapprove of upstaging the wedding party, or showing up looking like a clown.