Floyd Landis has been threatened with legal action if he does not withdraw allegations leveled at cycling leaders Hein Verbruggen and Pat McQuaid in a televised interview.

Verbruggen, who was president of the International Cycling Union for 14 years until being succeeded by McQuaid in 2005, said on Wednesday that the claims were "unacceptable."

"We cannot accept what he said and so that's it," Verbruggen told The Associated Press.

Landis, who was stripped of the 2006 Tour de France title for doping, told a German channel in November that the UCI had acted corruptly and protected some star riders from doping claims.

Verbruggen said a lawyer's letter to Landis invites him to apologize.

"It is unacceptable what he says and I think he is kindly invited to prove what he says," the Dutch official said.

The letter, which was first published by an American cycling website and dated Feb. 7, gives Landis 15 days to retract or face legal proceedings in Switzerland. Verbruggen and McQuaid's Lausanne-based lawyer wrote that the American's allegations were "detrimental to their honor."

The letter was disclosed Tuesday, hours after three-time Tour winner Alberto Contador was cleared of doping during his 2010 victory by the Spanish cycling federation. It had previously recommended a one-year ban for Contador, who tested positive for the banned drug clenbuterol that he claims came from contaminated beef.

Landis remained the only rider stripped of his Tour win for doping, though Contador could still lose his title. The UCI and World Anti-Doping Agency are weighing appeals against the Spanish decision at the Court of Arbitration for Sport.

The 35-year-old Landis retired from racing last month and claimed he was unable to find a job in the sport. Last May, his allegations of widespread drug use in cycling fueled an ongoing U.S. federal investigation that has targeted his former teammate Lance Armstrong.

Armstrong announced his own retirement Wednesday.