Credit-card issuers have drawn fire for jacking up interest rates on cardholders who aren't behind on payments, but whose credit score has fallen for another reason. Now, some consumers complain, Bank of America (BAC) is hiking rates based on no apparent deterioration in their credit scores at all.

The major credit-card lender in mid-January sent letters notifying some responsible cardholders that it would more than double their rates to as high as 28%, without giving an explanation for the increase