The US Department of Justice sued Visa for alleged antitrust violations on Tuesday, accusing one of the world’s largest payment networks of suppressing competition by threatening merchants with high fees and paying off potential rivals.Visa processes more than 60% of debit transactions in the US, bringing it $7bn each year in fees collected when transactions are routed over its network, the justice department said. The company protects that dominance through agreements with card issuers, merchants and compe ...