Originally Posted by Shareholder

It is not clear from the profile under his username if LPCjr is actually a STARGold. He doesn't show any UA profile (or a US one), and was referring to being a RCC member, which is a separate program from Mileage Plus. You should call the RCC customer service line to confirm this. I believe there is a reciprocal agreement with AC and UA to use one another's lounges if you have bought a RCC or MLL membership, separate from holding STARGold status. However, the terms of the agreement would restrict you to be flying either AC or UA, but not another airline, even STAR, though the receptionist may or may not know all the details.

However, as others have noted, if you are PremEx or 1K on UA, and thus a STARGold, then there is no problem as long as it is a STAR carrier you're flying.