Yes, there is a regulation, but first we need to establish the fact that the casino is not "buying back" your chips. The chips legally are and remain the property of the casino, and merely represent the money that you bought in for. You didn't "buy" them and don't own them physically.
Back in the old days, casino chips were used like an alternative currency in this town, used to pay for everything from groceries to haircuts. Although people still use them to chip, and chips still change hands privately between gamblers, especially high-stakes poker players, more than one player has run afoul of the rule that requires the casino not to redeem a chip if the player can't prove that it was originally given to them in exchange for their buy-in. That's what scuppered the plans of the so-called "Bellagio Bandit," who was unable to offload all the chips he stole, either to other players or at the casino cage. Legitimate players given chips in lieu of cash by other gamblers have suffered from the same problem.
Money-laundering prevention and a federal law that prohibits the creation of new currencies both conspired to clamp down on loose casino procedures in the chip department, requiring much closer scrutiny by casinos and their cashiers, so we (and the Gaming Control Board) would be intrigued to learn which casino told you it was okay to mail in your chips. Click the link to read the full scope of Regulation 12, which governs the creation and use of casino chips and tokens in Nevada. We called the Enforcement Division, just to make sure, and received confirmation that chips may only be cashed in person.
