Newly released records show the United States Postal Service spent US$31.9 million sponsoring Lance Armstrong's team during the height of the rider's Tour de France dominance.

Financial records obtained by ESPN through a Freedom of Information request revealed the previously undisclosed amount of Postal Service spending from 2001 to 2004, when the federal agency heavily promoted the rider. Armstrong won the Tour each year from 1999 to 2005. ESPN reported on the records Friday.

The sponsorship could become an issue in either a federal investigation into doping in professional cycling, or a federal whistleblower lawsuit that disgraced cyclist Floyd Landis has reportedly filed against Armstrong.

Landis has claimed Armstrong among others used performance-enhancing drugs, which - if found to be true - would have been a violation of their agreement with the Postal Service.

Armstrong has repeatedly denied doping, and his attorneys have said there never was any wrongdoing regarding the USPS sponsorship.

"Over the years, many different sponsors have seen - and continue to see - the benefits of associating with Lance and his cycling teams," Armstrong spokesman Mark Fabiani said in a statement.

Several Armstrong teammates and associates have appeared before a grand jury in Los Angeles that has been investigating pro cycling for months, but no charges have been filed.