Prime Minister Shinzo Abe may have tried to play down as an election issue his desire to revise Japan's post-war Constitution, but many opposition parties have seized on the deeply unpopular move.
Mr Abe's party, the Liberal Democratic Party (LDP), did not state this intent outright in its 26-page manifesto released this month.
But it has been pushed to the forefront of campaigning for the July 10 Upper House elections, alongside Mr Abe's economic policies.
The leading opposition Democratic Party, as well as other smaller opposition parties like the Communist Party, has vowed to block any attempt to revise the Article 9 clause which will allow Japan's Self-Defence Force to engage in overseas combat.
Yesterday, Social Democratic Party chief Tadatomo Yoshida said at a Shinjuku rally that this was the "biggest election issue", adding that a revision will "mark a 180-degree departure in Japan's position as a peace- loving nation, and is absolutely unacceptable".
Mr Abe yesterday said in Kumamoto that any move to dissolve or limit the scope of the Self-Defence Force was "irresponsible", given the heightened security climate.
The chief of the LDP's junior coalition partner Komeito, Mr Natsuo Yamaguchi, meanwhile said last week that neither the Constitution nor the contentious security laws should be key issues in the polls. "A nationwide debate over the issue of constitutional revision is so immature at this point that I don't think voters should be pressed to choose what they want to do with it."
The LDP and its coalition allies need to win 78 of the 121 seats up for grabs - giving them a two-thirds majority - at the polls to open the door to revise the Constitution.
Any formal amendment will need the approval of at least two-thirds of both the Lower and Upper Houses of Parliament, as well as a majority of voters in a public referendum.
Mr Abe's ruling bloc already controls a two-thirds majority in the Lower House.