The World Anti-Doping Agency said Tuesday it will challenge the Mexico Football Federation for clearing five players of doping after accepting that contaminated meat caused their positive tests for clenbuterol.

WADA said it had appealed to the Court of Arbitration for Sport, and would not comment further.

The Mexico case is WADA's second high-profile challenge to a legal defense of eating tainted meat.

WADA and the International Cycling Union appealed to CAS after 2010 Tour de France winner Alberto Contador blamed contaminated steak for his clenbuterol positive, and was exonerated by the Spanish cycling federation. That case is scheduled to be heard in November.

The five Mexico players tested positive for the banned anabolic agent at a May training camp before the Gold Cup.

Goalkeeper Guillermo Ochoa, defenders Edgar Duenas and Francisco Rodriguez, and midfielders Antonio Naelson and Christian Bermudez missed the tournament but were not punished.

The World Anti-Doping Code typically requires suspensions of up to two years for first-time offenses, or four years in cases of systematic doping programs.

CAS has not set a date for the hearing.

FIFA President Sepp Blatter backed Mexican officials' decision to excuse their players, saying ''it's definitely a case of food contamination.''

Mexico President Felipe Calderon has acknowledged that contamination with clenbuterol is a problem in the country, where it is used to bulk up livestock.

Clenbuterol is banned for use on animals in Europe.