Actually, it depends.

On the star alliance website:

"United Airlines' Premier Executive and Premier Executive 1K customer and US Airways' Chairman Preferred and Gold Preferred customers have access to U.S. domestic United Red Carpet Club and US Airways Club locations only when they present a ticket or boarding pass for a same-day international flight."

So, yes, if you are flying international (even in Y). But, no, if you are flying domestic (regardless of class of service)