At one time, someone told me that there was a case that a plaintiff won based on the legal restriction that only financial institutions (banks, credit unions, credit card issuer , those are federally licensed) are allowed to charge "interests", and that the defendant, a large corporation which is not a financial institution, is not allowed to collect "interests" from customers.
May be the law has changed, or may be it is not in the same jurisdiction or not in this case.
I recall soon after that, many large corporations which are service providers and what not, have changed wordings to their "late payment penalty fee", to not include the word "interests", but more as a penalty fee.