A total of 337 people plan to run in the upcoming Upper House election and vie for 121 of the chamber's 242 seats, according to a recent survey.

Prime Minister Shinzo Abe's Liberal Democratic Party and its coalition partner, New Komeito, are aiming for a majority that will give them control of both chambers of the Diet.

The ruling coalition already controls the more powerful Lower House, and the Upper House is in the hands of the opposition.

The six-year term of the 121 Upper House members expires July 28 and the election will likely be held July 21, according to the Public Office Election Law.

The major campaign issues are likely to be constitutional amendment, the Trans-Pacific Partnership free-trade talks, economic policy, disaster recovery and reactor restarts.

The tally, conducted by Kyodo News, showed Thursday that the total number of potential candidates had risen by 21 since the previous survey three years ago, but that the number of candidates to be fielded by political parties had fallen by 16.

Of the 121 seats, 73 are to be filled from the 47 prefectural constituencies and 48 through the proportional representation system, with each voter casting two ballots.

By party, the LDP has picked candidates for all prefectural districts.

But the opposition leader, the Democratic Party of Japan, is still reeling from the drubbing it took in the Lower House election last December and hasn't yet completed its candidate roster for those districts.

Opposition party Nippon Ishin no Kai (Japan Restoration Party), coheaded by Osaka Mayor Toru Hashimoto and former Tokyo Gov. Shintaro Ishihara, will jointly field candidates with Your Party in some constituencies.

The upcoming race will be the first national election to allow the use of Facebook, Twitter and other social networking websites in Japan.