His team immediately fired him, the International Herald Tribune reported.
Landis also may become the first Tour champion in the race's 103-year history to be stripped of his title because of doping allegations.
"The analysis of the sample B of Floyd Landis's urine has confirmed the result of an adverse analytical finding notified by the anti-doping laboratory of Paris on 26th July, following the analysis of the sample A," the International Cycling Union said.
The governing body added it would ask the USA Cycling Federation to open disciplinary proceedings against Landis.
Landis repeated his denial Saturday that he took performance-enhancing drugs.
"I was the strongest man in the Tour de France, and that is why I am the champion," Landis, 30, said, adding he would fight the charges and clear his name.
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