Japan's main opposition Constitutional Democratic Party plans to grill the government on its scheme to raise taxes to cover a bigger defense budget at the upcoming Diet session.

The party's Diet affairs chief Azumi Jun met on Wednesday with his counterpart from the main governing Liberal Democratic Party, Takagi Tsuyoshi.

Takagi told Azumi the government plans to convene an ordinary session of the Diet on January 23, and sought cooperation on issues such as deliberations on the draft budget for the next fiscal year.

Azumi expressed criticism of the government for announcing key policies, such as tax hikes for an increase in the defense budget, without explaining them in the Diet.

Last year, the government revealed that it would increase annual defense budget to about 2 percent of the country's gross domestic product by fiscal year 2027. The government plans to set total defense spending for the next five fiscal years at around 300 billion dollars. The money will come from tax increases to be imposed in 2024.

Japan's two governing parties agreed in December to levy an additional tax of 4 to 4.5 percent across the board on corporate taxes, while taking measures to limit the impact on small and midsize businesses. They plan to raise income tax by 1 percent.

Azumi said his party will challenge the government on the issue through Diet deliberations, and seek a detailed explanation.

Takagi told reporters he will work with a sense of urgency for smooth Diet procedures, as the government will be submitting key bills during the upcoming session.