An organization representing professional riders has blasted doping watchdog Dick Pound for alleged defamatory comments about widespread cheating in cycling, threatening to take further action if he does not publicly retract his allegations.

The Switzerland-based group, known by its French name, Cyclistes Professionnels Associes (CPA), has given the Montreal lawyer until January 20 to apologize for the comments, published last year in the Britain's Guardian newspaper, in which he accused riders, teams, organizers and officials of supporting a culture of "deliberate cheating" in the sport.

The outspoken Pound, head of the World Anti-Doping Agency, also had well-publicized spats with the world cycling's governing body, the UCI, and American Lance Armstrong last year.

"You have openly attacked the sport of cycling and its figures, claiming in particular the general existence of doping among cycling teams," the riders' association wrote in a letter to Pound, excerpts of which were published Wednesday in the Guardian. The Associated Press later obtained the full text.

"You publicly accuse all cyclists of acting against honor and sporting ethics, and branding them in the eyes of the public as cheaters bent on breaking the rules," the group said in demanding a public retraction. "Otherwise, the CPA could proceed by any means necessary."

The letter refers to an opinion piece written by Pound in October, in which he called the problem of doping in cycling a "stunning indictment of failure on the part of officials, organizers and riders."

"Drug use, within entire teams, continues unabated," Pound said. "It is planned and deliberate cheating, with complex methods, sophisticated substances and techniques, and the active complicity of doctors, scientists, team officials and riders. There is nothing accidental about it."

But the riders disputed Pound's allegations, calling them "particularly serious, disrespectful and defamatory."

Pound also accused the UCI of allowing doping to remain widespread.

"All this cheating goes on under the supposedly watchful eyes of cycling officials, who loudly proclaim that their sport is drug-free and committed to remaining so," Pound wrote. "Based on performance, they should not be allowed outdoors without white canes and seeing-eye dogs."

UCI rejected the allegations and said it was seriously tackling banned substances in cycling.

Pound has been at the center of much of the controversy in the cycling world since the French newspaper L'Equipe claimed in August that traces of performance-enhancing drug EPO were found in a set of Lance Armstrong's backup samples at the 1999 Tour de France.

Pound accused then UCI president Hein Verbruggen of leaking documents about the alleged positive tests to L'Equipe. Pound also questioned the union's willingness to fully investigate the allegations.

Verbruggen denied Pound's accusations and claimed WADA was blocking its investigation by withholding information.

Armstrong's agent and lawyer later criticized Pound, accusing the Canadian of smearing Armstrong in public without conclusive proof or due process.

Armstrong said he was concerned Pound might have been seeking revenge for an open letter he sent to newspapers and the WADA chief several years ago, defending his sport against the widely held notion that cycling was rife with performance-enhancing drugs.