USA Cycling said on its website on Thursday that it had been contacted by the International Cycling Union (UCI) regarding American Hamilton's alleged involvement.

"We received a communication from the UCI today containing the 'Operation Puerto' dossier for Mr. Tyler Hamilton and a request to open disciplinary proceedings against him," Steve Johnson, chief executive officer of Colorado-based USA Cycling, said in a statement.

"As required by our anti-doping regulations, we have forwarded the complete dossier to the U.S. Anti-Doping Agency (USADA) and have asked them to adjudicate this case on our behalf."

More than 50 riders, including 1997 Tour de France champion Jan Ullrich and Giro d'Italia winner Ivan Basso, have been linked to the probe. Nine riders including favourites Ullrich, Basso and Francisco Mancebo were withdrawn on the eve of this year's Tour de France for alleged involvement in the scandal.

Hamilton, who tested positive for blood doping at the Tour of Spain in September 2004, has denied charges that he injected another person's blood to improve his performance but the Court of Arbitration for Sport (CAS) upheld his two-year USADA ban.

Cycling is still reeling from this year's Tour de France champion Floyd Landis testing positive for testosterone, the banned male sex hormone, during the race.

The former Phonak rider has repeatedly denied taking performance-enhancing drugs.