Opposition parties went on the offensive Tuesday and forced the suspension of key Upper House committee sessions, boycotting them in protest against the Finance Ministry's refusal to disclose the master copies of ministry documents related to a controversial land sale deal with Osaka-based school operator Moritomo Gakuen.

The Asahi Shimbun has reported that two internal documents were revised by ministry officials before being disclosed to lawmakers seeking information on the sale — concluded at a huge discount — of the land plot in Toyonaka, Osaka Prefecture.

The Asahi report alleged that the later versions left out key information on the sale. If that is true, it would deal a huge blow to the ministry and possibly the whole of Prime Minister Shinzo Abe's Cabinet.