House Financial Services Committee Chairman Barney Frank expressed concern to the Federal Reserve that regulations limiting interchange fees could increase the regulatory burden on credit unions and other small financial institutions.

In a letter mailed Wednesday, Frank (D-Mass.) wrote Federal Reserve Chairman Ben Bernanke that the regulations "if not properly crafted, may have unintended consequences for consumer choice, the protection of consumer information, and Congress' intent to reduce the burdens on community banks, credit unions and government benefit programs."

The Fed's proposed rule capped debit interchange at no more than 12 cents per transaction. This would be a flat fee whereas debit interchange is currently calculated as a percentage of a transaction, often around 1%.