In Texas, it is against the law for a merchant (in this case, property management) to charge a fee for credit card use. See attachment. However, it does not effect a credit card company charging a fee. Just the merchant. This is a letter from the OCCC (Office of Consumer Credit Commissioner). It is dated 2011, but is still in effect.
Your question would definitely be one I would speak to an attorney about since finance codes vary from state to state. Hope this helps you...and all of you reading! ;)