Tyler Hamilton, whose two-year ban for blood doping is due to end on September 22, is now facing another investigation, USA Cycling said today (AEST).

A statement from the US federation said it has received information from the International Cycling Union (UCI) "regarding Tyler Hamilton and his alleged involvement in 'Operation Puerto', along with a request to move forward with disciplinary action".

"Operation Puerto" was the Spanish doping affair that saw 13 riders, including Italy's Ivan Basso, Germany's 1997 Tour de France winner Jan Ullrich and Spain's Francisco Mancebo suspended by their teams days before the start of the Tour de France, due to their alleged implication.

The nature of Hamilton's alleged involvement was not specified by USA Cycling, but evidence from the ongoing probe suggests he spent more than 30,000 euros ($51,000) on a doping program.

Hamilton has denied working with Spanish doctor Eufemiano Fuentes, who is central to the affair, but Spanish authorities claim they found several documents showing that Hamilton was one of Fuentes's best clients.

USA Cycling said today it has referred the matter to the US Anti-Doping Agency.

"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," said Steve Johnson, chief executive officer of USA Cycling.

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

USADA, which has a policy of not commenting on active cases, could not immediately be reached.

Hamilton, a former Phonak, CSC and U.S. Postal rider, had voiced a wish to return from his ban to compete in the world championships later this month, but had already been ruled out of the US team by USA Cycling.

Hamilton, also formerly of the retired Lance Armstrong's now defunct team, US Postal, was caught doping at the 2004 Tour of Spain after blood tests showed evidence of blood doping.

A dispute ensued over the validity of his Olympic gold medal, but he was allowed to keep the title after a second "B" sample was mishandled and rendered unsuitable for counter-analysis.

Hamilton denies allegations he injected another person's blood to improve his performance, and mounted an expensive - but ultimately unsuccessful - legal defence and publicity campaign in an effort to have the ban overturned.

The Court of Arbitration for Sport (CAS) ruled in February to uphold the two-year USADA ban.

The UCI said earlier this month that he would also be banned from the Pro Tour for a further two years, under the UCI Pro Tour teams' code of ethics.

USA Cycling officials have declined comment on the case, but did release the following statement on Thursday afternoon:

USA CYCLING STATEMENT REGARDING TYLER HAMILTON AND "OPERATION PUERTO"Colorado Springs, Colo. (September 14, 2006)--USA Cycling received information today from the UCI regarding Tyler Hamilton and his alleged involvement in "Operation Puerto" along with a request to move forward with disciplinary action.USA Cycling has immediately referred the case to the U.S. Anti-Doping Agency for adjudication."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," said Steve Johnson, chief executive officer of USA Cycling. "As required by our anti-doping regulations, we have forwarded the complete dossier to the U.S. Anti-Doping Agency and have asked them to adjudicate this case on our behalf."All inquiries regarding this matter should be referred directly to the U.S. Anti-Doping Agency. USA Cycling will have no further comment on this case.