Class-action suits were filed against three airlines.

The suits, against United Airlines, American Airlines and Trans World Airlines, were filed on behalf of members of the airlines’ frequent flier programs by attorneys for Eric Fuller, owner of a frequent flier coupon firm in San Diego who is involved in litigation with the carriers. The lawsuit, which seeks $500 million, claims that the airlines have reduced the value of the frequent flier discount coupons by designating them as non-transferable.