Legal Question in Business Law in Pennsylvania

You must first see if the creditor in writing disscussed that late fees would be charged and the amount of the late charges. If they are not in the contract or credit agreement or in some writing then the person claiming the amount due should not be able to charge a late fee. If there is a writing authorizing a late fee and you had notice of it the question then becomes is it reasonable or a penalty which may be illegal. Or it is possible the charge is excessive and otherwise not legal.