The U.S. Anti-Doping Agency says its review board has made a unanimous recommendation to file formal doping charges against Lance Armstrong.

That will move the case to an arbitration hearing if Armstrong chooses to challenge, as he has indicated he would.

USADA confirmed the board's recommendation Friday after one of its members, Clark Griffith, told The Associated Press he "can't wait" to see what the arbitration panel thinks of the evidence.

USADA says it has evidence Armstrong was taking performance-enhancing drugs while winning the Tour de France from 1999-2005. Armstrong says he is innocent.

Earlier in the day, Armstrong had gone on the attack against Griffith, using his Twitter account to note that the Minneapolis attorney had earlier this year been charged in a misdemeanor case of indecent exposure.

"Wow. @usantidoping can pick em. Here's ... 1 of 3 Review Board members studying my case," Armstrong tweeted, linking to an online story about Griffith.

Griffith entered an Alford plea on June 13. Under the plea, Griffith did not admit doing anything wrong but acknowledged prosecutors have enough evidence for a jury to convict him. A 24-year-old student reported Griffith unzipped his pants in front of her on a St. Paul street.

Sentencing is scheduled for July 26. Griffith told the AP he's innocent and entered the plea to avoid a trial that would embarrass his family.

Griffith said Armstrong's tweet was "an effort to get away from the issues that will be dealt with by an arbitration panel. OK? By smearing me, that does nothing. I'm innocent of that."

USADA has not publicly released most of its evidence against Armstrong. Griffith would not discuss Armstrong's case in detail but said, "He's really scrambling ... I can't wait to hear what the arbitration panel thinks of the evidence."

A spokesman for Armstrong declined immediate comment.