Leading U.S. airlines, including American Airlines $AAL, United Airlines $UAL, and Southwest Airlines $LUV, have voiced strong opposition to a renewed legislative push that seeks to cap interchange fees charged by credit card giants Visa $V and Mastercard $MA. In a formal letter to U.S. senators, the aviation industry warned that the proposed legislation could undermine the economic foundation of rewards-based credit cards, potentially leading to the end of frequent flyer miles programs that are crucial to customer loyalty and airline revenues.