Re: nested tickets on codeshared/alliance airlines. Has any airline out there attempted to claim that back-to-back tickets using its alliance partners are a violation of fare rules? Example: I buy a CO ticket on CO metal nested inside a NW ticket on NW metal. Seems perfectly fine to me as I am doing business with two separate companies.

If the airlines try to use their codeshare agreements to extend the tentacles of their fare rules, I would think The Feds would say "Now you are acting too much like one business. Back off a little bit."