American cyclist Tyler Hamilton faces a new doping investigation, less than two weeks before his two-year suspension for blood doping is lifted.

USA Cycling said Thursday it was contacted by UCI, which provided documents on Hamilton's involvement in a Spanish doping scandal. The sport's governing body also requested that USA Cycling open disciplinary proceedings against Hamilton.

``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,'' said Steve Johnson, chief executive officer of USA Cycling, in a statement.

``Operation Puerto'' erupted in May when five people _ including Spanish doctors Eufemiano Fuentes and Jose Merino Batres _ were arrested and charged when police seized drugs and frozen blood at a Madrid clinic. The samples were thought to have been prepared for performance-enhancing transfusions.

Hamilton, who tested positive for blood doping at the Spanish Vuelta in September 2004, will finish serving a two-year suspension for blood doping on Sept. 22. He has long denied he used blood doping, the transfusion of extra blood that can increase endurance.

Hamilton did not immediately return a message left on his cell phone or respond to an e-mail seeking comment.

In June, Spanish daily El Pais reported Hamilton was a client of Spanish doctor Fuentes. The article showed a copy of a fax, allegedly sent to Hamilton's wife _ Haven Parchinski _ detailing a doctor's bill for US$54,060. The report said Hamilton also had been sent two pages of doctors' files detailing calendars with medications to be taken in advance of the 2003 season.

Hamilton was not only engaged in banned blood transfusion practices, but also used EPO, anabolic steroids and human growth hormones during his treatment by Fuentes, the El Pais article said.

In a lengthy statement dated August 2006 on his Web site, Hamilton says he has been unable to get copies of the documents detailed in that article.

``What I do know is that these allegations are hurtful and false,'' Hamilton wrote. ``It is not clear to me who is translating and alleging these things. I have never even heard of some of the substances listed within these supposed `schedules'.''

Hamilton denied in June that he had been treated by Fuentes.

Nine riders, including 1997 Tour de France champion Jan Ullrich, Ivan Basso and Francisco Mancebo, were forced to withdraw before the start of this year's Tour de France because of alleged ties to Fuentes.

Hamilton won a gold medal at the Athens Olympics and once was considered a possible successor to seven-time Tour de France champion Lance Armstrong.