The International Cycling Union (UCI) criticised the decision by respected French sports daily L'Equipe to publish results from dope tests taken on the eve of the 2010 Tour de France.
"The UCI has been informed that the L'Equipe newspaper was going to publish in its edition on Friday a condidential document containing the riders' individual readings following tests carried out before the start of the 2010 Tour de France," said the UCI.
"First of all, the UCI deplores that this document has come into the possession of outsiders as it is a single tool on which the antidoping services organise their activity during the race.
"This document was reserved for the UCI and independent experts of the World Anti-Doping Agency (WADA). Such a weakness in the confidentiality is very serious and the UCI will open an inquiry to discover the origin of the leak."
Before the start of the 2010 Tour de France in Rotterdam, all 198 riders submitted to blood tests.
Elite riders have become used to such a system being carried out at various times of the season as part of the biological passport introduced in 2008 by the UCI.