Prosecutors have arrested Sadao Usuda, chairman of the Japan Dental Association, and Takeshi Shimomura, a member of a government advisory body, in connection with bribes the former allegedly paid to the latter for lobbying efforts aimed at boosting dental-service fees.

The bribery affair may hamper Diet debate on pension reform, because the opposition camp is demanding answers before debate proceeds. Shimomura, a member of the Central Social Insurance Medical Council, formerly served as chief of the Social Insurance Agency.

Five others, including Katsutoshi Kato, another member of the medical council, have also been arrested in connection with the case, investigative sources said. Kato, 59, also serves as a vice chairman of the Japanese Trade Union Confederation (Rengo), the nation's largest labor organization.