Sen. Roger Marshall is threatening to hold up a vote on the annual defense policy bill unless his amendment targeting credit card swipe fees is included, according to four sources with knowledge of the situation.

Marshall refused to confirm that on Thursday, telling reporters “that folks from the retail industry have worked this issue so hard up here that we have enough signals that we’re gonna get this across the floor if you get a vote.”

The Kansas Republican reintroduced legislation with Sen. Dick Durbin (D-Ill.) last month to force the major payment networks to compete on the swipe fees that merchants pay in exchange for accepting credit cards.

The lawmakers have been trying to attach the measure to the National Defense Authorization Act — replicating a maneuver Durbin executed with the 2010 Dodd-Frank Act that capped fees on debit card transactions.

Wall Street and payment network lobbyists have blasted the bill in an intense campaign, arguing that it would benefit big box retailers at the expense of consumers. They’ve also claimed the bill would threaten the future of popular credit card reward programs.