Japan is voting in upper house elections seen as a referendum on new Prime Minister Naoto Kan and his party's 10 months in office.
Voters began casting ballots Sunday for half of the chamber's 242 seats.
Support for the ruling center-left Democratic Party of Japan rose after Mr. Kan took office last month, but quickly plunged after the new leader proposed doubling the sales tax from five to 10 percent to help reduce the national debt.
During his last day of campaigning Saturday, Prime Minister Kan said the sales tax will not be raised without seeking a popular mandate in the next lower house election, which must be held by late 2013.
The leader of the opposition Liberal Democratic Party said the prime minister has no clear vision of how to revive Japan's financial system while protecting the livelihoods of its people.
The Liberal Democratic Party has ruled Japan for most of the past 50 years. The Democratic Party of Japan swept to power last year on the promise of change. But former prime minister Yukio Hatoyama resigned last month after losing popular support for reneging on his campaign promise to remove a U.S. military base from Okinawa.
The DPJ will remain in power regardless of the vote in Sunday's election because it holds a majority in the powerful lower house.
The ruling coalition still needs a majority in the upper chamber to avoid deadlocks and to reduce the country's considerable public debt.