Grace periods may vary, but usually range from 20 to 50 days depending on the type of credit card and the issuing bank.

The issuing bank gets repaid when the customer pays his credit card bill.

As credit-card operators they collect a fee on every transaction, whereas the issuing banks are left to collect interest or worry about bad debts.

Yet the law does not set absolute limits on rates and fees, which issuers have real incentives to raise.

University officials say that their agreements with card issuers comply with the law and bring in valuable revenue.