The case will go to an arbitration hearing if Armstrong, who claims he has passed more than 500 drug tests, chooses to challenge - and the cyclist has indicated that he will.

The USADA review board decided unanimously to file charges against Armstrong, who won the Tour de France from 1999-2005 for a total of seven consecutive wins. If the charges are proven, Armstrong could be stripped of his Tour de France titles.

The USADA has not yet publicly released most of its evidence against Armstrong.

Armstrong's spokesman declined immediate comment, but his lawyer wrote in a letter that the "USADA has no regard for its own protocol, fairness or common notions of decency."

The letter also accused two of the key witnesses against Armstrong, former teammates Floyd Landis and Tyler Hamilton, of being self-confessed dope cheats.

The USADA has pegged its case on those witnesses. In the letter, Armstrong's lawyer writes that the agency's alleged evidence includes previously disclosed emails from Landis and a 2011 television interview with Hamilton.

Armstrong's lawyers are trying to discredit any evidence the USADA uses from his former teammates, arguing that Landis is an admitted liar.

The USADA had previously announced, however, that at least 10 of Armstrong's former teammates and associates would testify against him, but the review board vowed to keep the names confidential.

A three-person arbitration panel could start considering Armstrong's case by November. The cyclist would be allowed to review the USADA evidence in advance and cross-examine any witnesses against him.

mkg/tm (AP/AFP)