The opposition Democratic Party boycotted Diet deliberation Friday on the Trans-Pacific Partnership after it obtained a manuscript of memoirs authored by former farm minister Koya Nishikawa. The book, which was to be published next month, reveals details of what went on in negotiations behind closed doors.

Prime Minister Shinzo Abe’s government has rejected repeated calls from the DP and other opposition parties to disclose the horse trading that went on in getting agreement on the TPP.

Apparently shaken by the stir his book has caused, Nishikawa later told reporters he will not send it into print.

The book, titled “The Truth about TPP,” was slated to hit bookstores in May. Nishikawa chairs the TPP special committee that is currently deliberating ratification of the TPP and related domestic bills.

DP lawmaker Yuichiro Tamaki, who obtained the manuscript, first brought up the issue in the Diet on Thursday.

Tamaki said the book reveals that U.S. negotiators offered concessions one month before U.S. President Barack Obama visited Japan in April 2014.

The DP is indignant that lawmakers were unaware of this until now. Documents they had access to were largely redacted and contained no mention of the supposed U.S. offer.

On Friday, fellow DP lawmaker Rintaro Ogata asked in the Diet whether officials at the Ministry of Agriculture, Forestry and Fisheries or the Cabinet Secretariat cooperated with Nishikawa on the book, as it includes details that were not previously made public.

Economic Revitalization Minister Nobuteru Ishihara, who replaced Akira Amari as TPP minister, replied that he could not comment — not least because the alleged manuscript may not be genuine.

DP lawmakers then walked out, saying the government had questions to answer and that Nishikawa was unfit to chair the committee.

Kyodo News said the book alleges Japan brokered a deal with New Zealand, which was seeking to expand its imports to Japan to more than 90,000 tons annually. Tokyo replied that it would agree to this if Wellington helped to persuade Washington to remove tariffs on Japanese cars much earlier than the U.S. was offering. Washington made no concession, and the deal did not go through.

Ahead of the Upper House election this summer, the DP, the biggest opposition party, is taking every opportunity possible to attack the LDP. The latter is playing the election with an aim of revising the Constitution.

Yet the DP, which was born only last month from the merger of two parties, has already stumbled amid a political funds scandal involving its policy chief, Shiori Yamao.

Although the DP sees the TPP as offering opportunities to attack the ruling coalition, it is unclear how substantive the deliberations will be.

Former TPP minister Amari is absent, citing a sleep disorder. He was Japan’s principal negotiator but quit amid allegations of cash-for-favors involving ministerial staff.

It is also unclear if the Diet can summon Koij Tsuruoka, who was the nation’s chief civil servant negotiator, as he has been appointed ambassador to the United Kingdom and will leave for London in less than a month.