The changes, according to Amex spokesman Vanessa McCutchen, were prompted by a desire to enable consumers to directly deposit government payments, such as those from Social Security, to the card. 

"As we've begun to gain scale with Bluebird and listened to our customers, it was clear that the ability to load federal payments and benefits directly to Bluebird accounts was something our customers were very interested in," wrote McCutchen in an emailed response. "Regulations allow federal payments, such as tax refunds and Social Security payments, to be directly deposited into a prepaid card account only if  the card is set up to meet the requirements for FDIC insurance coverage." 

The FDIC-insured bank that has agreed to hold the deposits is Wells Fargo, but the bank did not return calls for comment as of press time.

NAFCU CEO Fred Becker noted that the even with a pass-through arrangement, the fact the Bluebird funds carry FDIC insurance opened the cards up to regulation from the FDIC and from the Consumer Financial Protection Bureau, which has already come down on American Express about discrepancies in disclosures around some of its products.

"I don't think American Express can assume it's only heard from Mr. Cordray once," said Becker, referring to CFPB Director Richard Cordray. The CFPB is in the process of developing a regulation addressing prepaid cards.

The Independent Community Bankers of America, long a credit union opponent and a leader in the effort to keep Walmart from obtaining a bank charter, expressed displeasure at the move. The association takes a very dim view of FDIC insurance covering  money added to Bluebird cards, according to Viveca Ware, senior vice president for regulatory policy at ICBA. "These cards are nothing more than checking accounts in prepaid clothing and need to be regulated as such," she said.