On the same day a merchant group's study claimed retailers pass on interchange savings to consumers, debit card issuers released their own study that claims merchants do no such thing.

"As part of their lobbying tactics, giant retailers promised to lower prices for their customers if Congress passed the Durbin amendment. Two years after implementation, retailers have taken home an $8 billion annual windfall while their customers still aren't seeing a discount for using debit," said Sam Fabens, spokesman for the Electronic Payments Coalition, which sponsored the study.

To collect the data for the field research, 32 shopping trips were performed at 16 stores nationwide. Identical products were purchased at each store and compared: one shopping trip in September 2011 before implementation of the Durbin amendment; one in September 2012 – a year after the implementation of the Durbin amendment; and one in September 2013 – two years after the implementation of the Durbin amendment.