The Internal Revenue Service reiterated its demand for casinos and other poker tournament sponsors to begin reporting winnings of more than $5,000 after March 4, 2008. The IRS and the Treasury Department originally issued guidance on Sept. 4 about the requirement, but the IRS is seeking to publicize it further. For tournaments completed during 2007 and before March 4, 2008, the sponsors are not required to report the winnings to the IRS or withhold tax. Beginning March 4, however, all tournament sponsors need to report winnings of over $5,000, usually on a Form W-2G.

Tournament sponsors who comply with the reporting requirement don't need to withhold taxes on the winnings. If the sponsor does not report the winnings, though, the IRS will enforce the reporting requirement and require the sponsor to pay any tax that should have been withheld from the winner. The withholding amount is normally 25 percent.

Tournament winners must provide their taxpayer identification number or Social Security number to the tournament sponsor. If they don't, the sponsor must withhold 28 percent of the winnings. Taxpayers must also report their winnings on their own to the IRS, as they have been required to do in prior years.