A former railway union official from Saitama was arrested Friday for allegedly threatening and harassing a member into quitting the union and ultimately the company.

Satoru Yamada, 29, a former official of the union of workers at East Japan Railway Co., is suspected of coercing the 28-year-old motorman last year, police said.

Yamada was head of a youth chapter of the union in Omiya, Saitama Prefecture.

Police also arrested Shuichi Saito, 30, and three other union members in connection with the case.

They said they have obtained arrest warrants for two other members of the union and are questioning them in connection with the case. They also searched the headquarters of the union in Shibuya Ward, Tokyo.

According to investigators, Yamada collaborated with several other members of the union chapter believed to belong to the radical Kakumaru Faction leftist group.

They are suspected of coercing the motorman into leaving the union in late February and eventually quitting JR East in late July. The union members allegedly harassed and threatened him in groups at the workplace on dozens of occasions until the motorman became ill.

The JR East labor union was formed after the 1987 breakup and privatization of the Japanese National Railways. It drew members chiefly from the former Nihon National Railway Motive Power Union (Doro), who have taken a nonconfrontational stance with management.

Doro split in 1951 from Kokuro, the National Railway Workers Union, the main union for the JNR workers. Doro was seen by public safety authorities as the most left-leaning union under the influence of the Kakumaru Faction.

The union, led by Kozo Kadogishi, has some 55,000 members.