The U.S. Department of Justice (DOJ) is preparing to file an antitrust lawsuit against Visa Inc. ($V), accusing the company of illegally monopolizing the U.S. debit card market through anticompetitive practices. The lawsuit alleges that Visa's actions have effectively shut out rival payment processors, thereby violating antitrust laws. This development follows reports from Bloomberg News and other news outlets highlighting the DOJ's intent to target Visa's market practices.