I disagree with this.

While having NPC unanimous agreements regarding recruitment and membership-related issues are great, I don't think it'd be a good idea to have an umbrella organization dictate who can or cannot wear letters. That should be totally left up to the individual organization.

And btw, because I'm a nitpicker...if you're talking NPC, it's Panhellenic. Pan-Hellenic often refers to the Divine 9 -- the 9 historically Black Greek Lettered Organizations. It's funny how a - and H can totally mean something else.