If the case is successful in Belgium, it could undermine the work of the World Anti-Doping Agency and be used as a precedent to contest the ruling in other courts around the world.

Lawyer Kristof De Saedeleer represents a group of 65 soccer and volleyball players and cyclists. He has filed the case with Belgium's Council of State high court, which could take up to six months to rule.

Athletes are obligated to give their whereabouts up to three months in advance. Out-of-competition tests are essential in catching cheats since many illegal substances can become untraceable by the time competition starts.

To perform such tests, WADA needs to know at all times where and when athletes can be traced. Under the latest WADA code, athletes must specify one hour each day where they can be located for testing.

"It gives WADA a pass to invade the privacy of athletes," De Saedeleer said by telephone Tuesday.

Three missed tests or three warnings for failing to file such information within an 18-month period constitute a doping violation and can lead to a ban.

The Belgian challenge cites privacy provisions within the Belgian constitution and the European Convention on Human Rights and Fundamental Freedoms of the Council of Europe.

Although the athletes stress they do not object to out-of-competition doping, they claim the system is far too invasive, forcing them even to pinpoint when they go to the movies.