Finance Minister Taro Aso (Photo: AFP)

Six opposition parties held an urgent joint meeting in Japan's Diet on Wednesday over the Finance Ministry tampering with government documents and calling for Finance Minister Taro Aso to resign, reported Japanese media.

Opposition parties, which include the Constitutional Democratic Party of Japan and Democratic Party for the People, ensured in the meeting that there was no interference from Japanese Prime Minister Shinzo Abe who supported Aso remaining in his post.

An investigation around the controversial Moritomo Gakuen land scandal revealed that references to Abe and his wife were deleted from ministry documents, invoking criticism of the finance ministry and a call for resignation of the minister.

Aso has said he will return a full year's salary, but will not resign from his post.

In 2016, Moritomo Gakuen, a controversial nationalistic organization, whose founder was a staunch supporter of Abe, bought a plot of land at a sixth of the market value from the government to build a school.

Later, it was revealed that the prime minister's wife, Akie Abe, was listed as the school's honorary president.

After claims that Akie Abe was involved in lobbying the government to lower the price of the land, she resigned from the post.

In March this year, the scandal was thrust into the limelight again after information revealed Shinzo Abe and his wife were removed from the ministry documents linked to the scandal.

Aso said one senior official resigned and 20 others have been punished for the scandal.