Actually…
There are illegal bits for hunters at USEF shows, which are a cause for elimination.
Unconventional bits may be penalized, but are not cause for elimination.
From the USEF rules:
HU105 Tack
- Snaffles, pelhams and full bridles, all with cavesson nose bands, are required.
a. Judges may penalize, but may not eliminate, a horse or pony that competes in a snaffle, pelham, or full bridle that is unconventional. Unconventional snaffles, pelhams, or full bridles include, but are not limited to, hunter gags, kimberwickes, etc.
b. Judges must eliminate a horse or pony that competes in illegal bits or nosebands. Illegal bits include, but are not limited to, three rings, gags (other than the hunter gag), et cetera… Illegal nosebands include, but are not limited to, drop, flash and figure eight nosebands.