"An Illinois state law restricting interchange fees for certain payments threatens the national banking system by interfering with federal powers to regulate that system, the Office of the Comptroller of the Currency and a group of 10 former comptrollers said in separate court filings last week. The Illinois Interchange Fee Prohibition Act, or IFPA, bans banks, payment networks and other entities from charging or receiving interchange fees in Illinois on the portion of a debit or credit card transaction attributable to tax or gratuity."