A key campaign issue was Prime Minister Ichirō Hatoyama's plan to revise Article 9 of the constitution – any change of the constitution requires a two-thirds majority in both chambers of the Diet. The left parties aimed to win at least a third of seats to prevent any constitutional change. Another issue was the government's plan to replace the elected prefectural boards of education with appointed ones, a plan fiercely opposed by the left: In June 1956, on the LDP's request the police intervened in the "deliberations" in the Diet when Socialist Councillors resorted to violence.