I noticed that the interest rate on my card went up last month without any notice. Can they do that?
Your card issuer generally must give you 45 days advance notice before it raises your interest rate on new purchases; there are additional rules that restrict when the card issuer can raise your rate on your existing balance.
This does not apply if you had an introductory rate (such as a low rate on balance transfers) which expired, or if you have a variable rate and the index to which your rate is tied (for example, the U.S. Prime Rate) has increased.
If you believe your interest rate was increased in error, you should contact your card issuer.