Is it legal for credit card companies to add interest to your bill before invoice is received?

Most credit card companies have a grace period for new purchases. However, there are many extremely aggressive and predatory credit card plans out there. They have been given wide latitude by the government to take advantage of unwitting consumers. You need to review any correspondence you have regarding your account to see it that practice was mentioned. If not, you should report the matter to your state attorney general's office for a review. In the meantime you should make certain you make your payments. In fact, you should try to pay off the account in full. Other charges are sure to add up quickly.