Osaka Ishin no Kai (One Osaka) has announced that it will dismiss Osaka Prefectural Assembly member Kei Yamamoto from its ranks after revelations that he sent threatening messages to junior high girls via the Line texting app.

Yamamoto, 34, elected from the city of Katano, faces expulsion, the toughest penalty under the rules of the group, which is part of Nippon Ishin no Kai (Japan Restoration Party).

According to the board of education of Katano, Yamamoto became acquainted with about 20 junior high school girls at a local festival last October, by handing out his business card there. He got in touch with the girls through a chat group on Line, through which he invited them to a "tea party."

None of the girls showed up to the party, however, and he was subsequently removed from the chat group list.

That apparently got him angry, the board officials said, and he started sending threatening messages, such as "I won't forgive you for this," "I know the identity of each of you" and "I can call up the principal of your school."

The incident surfaced in November after one of the girls notified her school of the threatening messages.

Yamamoto apologized for the incident and shaved his head to "take responsibility." But Yutaka Imai, secretary-general of One Osaka, was unimpressed, saying the group's disciplinary committee concluded unanimously that he "lacked awareness that his action caused trouble to guardians of the girls and their schools."

The party was to send a letter to notify Yamamoto of the decision Tuesday. He has one week to appeal, and if he doesn't, the decision will become final then.