What are the withholding requirements for winnings from casino gambling?

The casinos do not withhold taxes from winnings. They issue the player a Form 1099G, which shows the players jackpot amount, a copy is filed with the IRS and the player is responsible for reporting the winnings when the file their taxes. Casino gambling winnings are considered income by the IRS. The only time taxes are withheld from winnings at the time jackpots are paid is from the multi-million dollar jackpots. A representative from the IRS is present at the time payment to the player is made. It can take hours for one of those to be paid, as they are not paid by the casino but rather the company that makes the slot machine, such as IGT or Bally's.

Different states have different laws on this also. For example, Indiana withholds 3.4% state tax from all jackpots of $1200 and up. You can request federal tax be taken out at the time you are paid also, but beware: federal tax is 25% of the jackpot, so unless you hit a really nice jackpot ($20,000+) you probably don't want to take Federal out.