Who are the mob stealing from in Casino?

There's two sets of "stealing" going on....

1. The Skim

The point of the "skim" is to hide the income from the Tax / Revenue Services

Skimming refers to the illegal transfer of funds from casinos to outside personnel without official documentation. Skimmed money is usually transferred in cash to evade taxes and to fund organized crime anonymously. The quantities of money skimmed are usually small portions of the casino's total profit so as not to arouse suspicion from regulators or law enforcement.

^{Skimming @ Wikipedia}

Since the money is removed before it goes through the 'official' counting process it's not taken into account by tax officials nor does it show in the casino's books.

Taking advantage of gaming laws that allow him to work in a casino while his gaming licence is pending, Sam doubles the casino's profits, which are skimmed by the mafia before they are reported to income tax agencies.

^{Casino @ Wikipedia}

2. Stealing from the Skim

The casino is owned by the Teamsters Union which is in turn controlled by the Chicago Mafia who want to "skim off" the cream of the money without the money coming to the attention of the tax authorities.

Being authorised to skim is one thing, that's OK by the Mafia who expect to get ALL the skim.

Stealing from the skim is stealing from the Mafia....that will get you killed.

Like most corporations, the The Tangiers Hotel Casino was (at least on paper) publicly owned by multiple entities and persons. The initial funding was provided by the Teamsters Union, which itself was controlled by the Chicago mob families. The union boss (Andy Stone) listened to and reported to the Dons. The Union received shares in the Casino and a dividend of the profits. The CEO of the Casino (Philip Green) was a clean guy they appointed & was a rubber stamp for all intents and purposes. The real controller on the ground was another mob affiliate appointed by the Teamsters: Ace Rothstein, the brilliant bookmaker.

So there's the network: the name sake CEO (Phil Green), the shareholders (Teamsters), the field controller (Ace), the real remote controllers (The Mob) and the muscle (Nicky Santoro).

The laws and regulations were set by the NGC, which itself held shady local characters. Even Ace could not get into the counting room, by law. The licensed men who worked the counting room, were appointed by John Nance, who was the Mob's courier. Nance could get in and leave once or twice a month with a bag & the cash skim. The skim was the cherry topping for the Mob and funded various activities.

No, they were not stealing from themselves literally. With the skim, they were stealing pre-tax revenue from the Casino, which in effect was stealing from both the Casino and taxes from the govt. off the books.

The union pension fund put up the money for the hotel and the casino, but the union officials were corrupt and with the help of the mob diverted some of the casino's profit into their own pockets. That money should've gone back to the union and help pay benefits to the members.

I believe that before the skim Tangiers was doing not really well. It may even belong to somebody else. By funding the New Tangiers the bosses could become de facto the directors and succeeded to put their men in (Green, Ace, the counting room skimmers). The film skimming steals taxes from the government which is tax evasion. That's why FBI got involved in the end.