Under California law, employers cannot require employees to patronize the business establishment they work in and must reimburse an employee for all business expenses necessarily incurred by the employee. It is also illegal to dock an employee's pay for cash shortages. If this is a California business, it is likely engaging in illegal practices.
However, if this is an Indian casino, it is probably not subject to California law. Indian casinos are subject to treaties with the U.S. government and your rights are most likely subject to those treaties or the tribe's laws itself. Very few attorneys practice in this area. But if there are any of my colleagues out there who do so, perhaps they can advise you.
Finally, if you belong to a union, you should discuss the matter with your union representative to see if these issues may be grievable.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
Mr. Kirschbaum is absolutely right about California law, but I have a feeling you work at a casino on a Native American reservation. That being the case, the answer to your question becomes much more complex, as the reservation is a sovereign nation not bound by the vast majority of state and federal employment laws.
You may need to consult with an attorney who specializes in tribal law--specifically the tribal law applicable to this particular reservation--if you want to be certain about your rights. You can use the Find A Lawyer function on Avvo to find such an attorney. Good luck.
This answer is a general interpretation of the law and is not fact specific to your case. Likewise it does not create an attorney-client relationship. You should seek an attorney for a review of your specific facts and documents. http://www.johnphillipslaw.com
I'd just add that you should get it documented by your employer that you are being requested to do this -- especially if your employee handbook doesn't allow you to play at the casino in which you work. While you're correct that this is common practice in the industry, it's also often used as a trap: you're verbally "allowed" by the pit boss or floor supervisor to play on a slow day, but your employment terms/handbook specifically disallows this, and they then use it as a reason to retaliate against you (in such a way that will hinder you from future employment in other casinos) should you burn the wrong bridges.
I focus my practice on (video) gaming industry, casino gambling, and complex internet law issues, electronic free speech, entertainment law, copyright and trademark law, and computer fraud. I primarily represent game developers and founders of emergent internet technologies. The author is a Maryland attorney; however no answer given on Avvo is intended as legal advice or intended to create an attorney-client relationship.