Join Date: Apr 2009
Location: Bye Delta
Programs: AA EXP, UA Silver, HH Diamond, IHG Plat, Hyatt Plat, Marriott Titanium, Nat'l EE, Avis PC, Hertz PC
Posts: 16,633
Most UP fares say something like this in the rules:
VALID FOR TRAVEL IN FIRST CLASS WHEN AVAILABLE.
IF FIRST CLASS IS NOT AVAILABLE - FARE IS VALID
FOR TRAVEL IN COACH CLASS.
I do not see any such language in the U fare that has the first/business booking codes.