"Our independent analysis indicates that when placed into practice, the interchange provision will do nothing but add to the bottom lines of big-box stores and giant retailers — all at the expense of consumers and small financial institutions," Becker said.
He said he wasn't aware of any threats made by MasterCard or Visa to his organization or its members.
Durbin asks for a reply to the letter by June 14.
The Senate passed Durbin's amendment May 13with a 64-33 vote. It grants retailers more control over the so-called "swipe fees" they must pay the credit card industry each time a customer uses a debit or credit card.
Updated at 6:15 p.m.