Education ministry officials said Friday that Japan's largest textbook publisher violated rules by showing an unapproved English textbook to teachers it paid, the latest in a series of revelations that have cast doubt over the fairness of the textbook selection process.

According to the ministry officials, Tokyo Shoseki Co. held an "editorial meeting" in September 2010 at a hotel in Nagoya that was attended by about 30 English-language teachers at junior high schools in western Japan. The publisher paid each teacher ¥10,000 ($85) for their feedback and also covered their transportation and accommodation expenses.

During the meeting, Tokyo Shoseki showed them an English textbook that was being screened by the ministry, despite rules prohibiting involvement by outsiders so as not to influence the screening process, said the Ministry of Education, Culture, Sports, Science and Technology. The textbook has been used since the 2012 academic year.

Tokyo Shoseki is the third publisher found to have broken those rules, after Sanseido Co. and Suken Shuppan.

Tokyo Shoseki, which reported the matter to the ministry Friday, is now investigating whether the meeting influenced the textbook selection process by local education boards.

Sanseido has admitted to holding similar meetings over past years. They were attended by 53 school personnel, including principals, who were each paid ¥50,000 as "editing fees."

Of those 53, 21 were found to have been later involved in choosing which textbooks to use in public schools from among those that had cleared ministry screening.