What conditional to use for an infraction group?

[Ombra]

I have a custom feature on my forum that I don't want users restricted by infractions to be able to use. Normally, to restrict access for a certain usergroup I would do this:

if (!is_member_of($vbulletin->userinfo, X))

This doesn't work for infraction groups though; I'm guessing because vBulletin only overrides their permissions with my restricted usergroup settings instead of actually moving them into the usergroup. So what do I need to use to block their access?

Note that this code is in a php file and not the template, in case that makes a difference.