Several justices questioned whether it is important to the case that many people earn and spend miles on items other than airline tickets. "Do we have to worry about that in this case?" Justice Samuel Alito asked.
Adina Rosenbaum, Ginsberg's lawyer, told the court that the growth of mileage programs to encompass more than airline tickets is another reason to rule that Ginsberg's lawsuit is not blocked by the deregulation law.
Breyer said the court perhaps could leave questions involving miles earned elsewhere "for another day."
A decision is expected by late June.
The case is Northwest vs. Ginsberg, 12-462.