Restaurant Is Saving Credit Cards And Drivers Licenses

My mom recently ate at a restaurant in TN, USA. She left the restaurant without the credit card she used to pay for her meal (she’s not sure if they even brought it back to the table or not). When she realized the card was missing the next morning, she called to ask if it had been found. She gave the name, number, and physical description. The employee insisted no cards were left the night before, and they did not have it. She went early before they opened and insisted her card had been left there. An employee took her to the register, lifted the tray, and revealed a thick stack of credit cards, and there were also two drivers licenses. He kept telling her they didn’t have the card she described, but lo and behold, she noticed it in the stack, snatched it, and left. Is what this restaurant is doing legal? What can we do to report them?