Police said Tuesday they had launched an investigation into a progressive group of unionized teachers for mass-mailing teachers in Seoul to ask for their participation in opposing Japan’s discharge of water from the Fukushima nuclear power plant.

The Seoul branch of the Korea Teachers and Education Workers’ Union reportedly sent out mass emails to 70,000 school teachers based in Seoul under the Seoul Metropolitan Office of Education last month urging them to take part in a signature campaign opposing the neighboring country’s plan to release its contaminated water from the nuclear power plant.

During the mass mailing process, the KTU reportedly tapped into K-edufine, a government-managed task management system for teachers, to access teachers’ email addresses saved in the system without gaining their approval or permission.

Late last month, the Education Ministry requested an investigation of the union by the Korean National Police Agency on suspicions of using teachers’ personal information without their consent. The KTU is also accused of breaching the state public officials act, which stipulates that teachers should remain politically neutral.

Under the country’s Personal Information Protection Act, a person can be subject to up to five years in prison or a fine of up to 50 million won ($38,300) if one uses personal information provided by a third party for other purposes.

Seoul’s Jongno Police Station is investigating the case whether the teachers’ union violated the personal information protection law and the state public officials act.

Police added that they would thoroughly investigate the mastermind behind the mass mailing scheme, the intention behind it and whether there was any misconduct in the process of obtaining teachers’ email addresses and sending them.