Although customer satisfaction with credit unions declined, the industry remains best in class for financial services and displays the top customer satisfaction benchmark among all service categories covered in the ACSI.

“Even with the drop this year, that score of 82 for credit unions is not only best in class among financial services but right up there at the top with companies such as hotels, retailers, online retailers” said David VanAmburg, ACSI managing director. “Credit unions are still considered one of the best service experiences.”

Moreover, credit unions continue to do better than small banks in customer satisfaction, while outperforming all of the big banks by a wide margin, according to the ACSI.

“Like small banks, credit unions offer more personalized service and fewer fees. This year, however, an influx of new clients causes credit unions to retreat from their past lofty standards for customer service,” the ACSI noted.

Because of a change toward more fees and higher minimum balance requirements, the ACSI said this could be worrisome given the industry's weaker customer service this year.

“The large influx of new customers for credit unions, many of whom left banks because of rising fees, poses new challenges for customer service,” said Claes Fornell, ACSI founder. “The question becomes how to best serve a fast-growing customer franchise. The more customers you have, the more difficult it gets.”

VanAmburg emphasized that it's not that credit unions are doing anything wrong. Rather, it's the nature of a commodity that is in demand. He compared it to when Apple debuted the iPhone. Consumers flocked to it, but customer satisfaction dropped.

“There was nothing wrong with the iPhone. So many people were signing up that it basically sucked up all of the bandwidth. AT&T couldn't manage all of those new customers,” VanAmburg explained. 

“I think that's what going to happen with credit unions. It's a good thing that they're getting business, but the question now is, How are you going to manage it?”

Meanwhile, banks have improved their customer satisfaction score since last year from 75 to 77. The ACSI said the higher score is mostly the result of continued high customer satisfaction with smaller banks, which have gained market share and therefore impact the industry average more in 2012. Smaller banks, defined as those banks outside of the big four, Bank of America, Citigroup, JPMorgan Chase and Wells Fargo, scored 79.

The other improvement factor for banks is a 6% increase in customer satisfaction for JPMorgan Chase, the nation's largest bank. JPMorgan Chase leads big banks with a score of 74 but still trails the small banks, which tend to offer more personalized service, free checking, and lower fees, according to the index.

Other big banks have had to deal with deteriorating customer satisfaction, the ACSI discovered. Compared to 2011's figures, Wells Fargo slid 3% to 71 and Citigroup retreated 4% to 70. Bank of America dropped 3% to 66, reaching its lowest level of customer satisfaction in over a decade, the data showed.

“The total fees from overdraft charges alone in 2011, most of them from big banks, amounted to more than $30 billion,” Fornell said. “Customers increasingly are rejecting the ever-mounting fees charged by large banks and taking their business to credit unions instead.”

Fornell said Bank of America, in particular, stands out as the only bank that is still below its prerecession customer satisfaction level. “It is clear that this is mostly because of fees.”