Visa exploits its market dominance to stifle competition, costing consumers and merchants billions in extra fees, feds allege.

The financial giant, which processes the majority of debit card spending in the United States, unfairly imposed fees on merchants and deterred rivals, the Justice Department said.

The U.S. Department of Justice has filed a lawsuit against Visa, alleging the company maintains an illegal monopoly over debit cards, while Senators Durbin and Marshall have introduced a bipartisan bill to address Visa and Mastercard's near duopoly over the credit card market.