Senator John Thune has proposed legislation to exempt from US income tax prices and awards won in the Olympic and Paralympic Games. The prizes awarded by the US Olympic Commission amount to USD 25,000 for gold, USD 15,000 for silver and USD 10,000 for bronze medals. Currently such awards are subject to the marginal income tax bracket of the individual sportsperson (maximally 39.6%). Whether the Bill will be brought further needs to be awaited. Apparently there is support from both parties and the White House.
Source: http://www.foxnews.com/politics/2014/02/25/senator-pushing-bill-to-keep-us-olympic-winners-from-being-taxed-on-prizes/, http://beta.congress.gov/113/bills/s2026/BILLS-113s2026is.xml