In a letter to federal authorities, a Wisconsin congressman equates the anti-doping charges against Lance Armstrong to a conspiracy theory and calls the U.S. Anti-Doping Agency's authority over the seven-time Tour de France winner "strained at best."

Rep. James Sensenbrenner, a Republican, wrote the Office of National Drug Control Policy on Thursday questioning the nearly US$10 million in public funding USADA receives, its procedures investigating and charging athletes with doping violations and whether it receives regular oversight.

USADA charged Armstrong last month with using performance-enhancing drugs while winning the Tour de France from 1999-2005. He maintains his innocence and sued in federal court to block the case from moving forward.

Armstrong's lawsuit claims USADA's arbitration process violates his constitutional rights to due process and that USADA doesn't have jurisdiction. Sensenbrenner's letter mirrored many of the issues raised in Armstrong's lawsuit and repeated his long-standing claim that he's never failed a drug test.

"The alleged lack of fairness raises concerns for athletes of all levels, the majority of whom lack the resources and platform to challenge USADA's actions," Sensenbrenner wrote. "The United States Congress has no role in determining whether an individual athlete doped, but we do have a great interest in how taxpayer money is spent .... USADA's authority over Armstrong is strained at best."

Created in 2000, USADA is recognized by Congress as the official anti-doping agency for Olympic sports in the United States.

USADA chief executive Travis Tygart said the agency's arbitration process is fair to athletes and he's willing to discuss the agency's funding and policies in detail with Sensenbrenner.

"The case against all those involved in the USPS Pro-Cycling Team Doping Conspiracy, including Lance Armstrong was not brought lightly. We are well aware of his popularity and the admirers he has on Capitol Hill and elsewhere, but our responsibility is to clean athletes who demand that USADA protect their right to a level playing field by eradicating drug use from sport," Tygart said.

"The evidence is overwhelming, and were we not to bring this case, we would be complicit in covering up evidence of doping, and failing to do our job on behalf of those we are charged with protecting," Tygart said.

Sensenbrenner has involved himself into controversial sports cases in the past. In 2004, he questioned whether the U.S. Olympic Committee had done enough to support American gymnast Paul Hamm in a gold medal dispute.

Armstrong's lawsuit against USADA is pending before U.S. District Judge Sam Sparks. The coach of his winning U.S. Postal Service and Discovery Channel teams, Johan Bruyneel, who also has been charged by USADA, faces a Saturday deadline to challenge the case in USADA's arbitration process or accept the charges and sanctions, which likely would include a lifetime ban from sports.

Also on Thursday, Michele Ferrari, an Italian doctor who was a consulting physician for Armstrong for years and was given a lifetime ban by USADA this week, said in a statement on his website he was not guilty of the charges.