Labour leader David Cunliffe has produced documents to prove he did carry out consultancy work on the formation of Fonterra.
However, fresh questions have arisen about his time at America's prestigious Harvard University.
Earlier this week National-aligned commentator Matthew Hooton said it was "untrue" Cunliffe had worked on the merger that produced Fonterra. Cunliffe had made reference to his work while with Boston Consultancy Group, in an interview with Fairfax Media.
Hooton, who was a communications consultant on the deal, insisted: "David Cunliffe had nothing to do with the foundation of Fonterra."
Cunliffe rejected his allegations, stood by his work history and criticised Hooton for making the claims without checking with him first.
This morning he provided documents to Fairfax Media which show he carried out work for the Dairy Board in the late-1990s. It appears on the electronic records under the new client name Fonterra Co-operative Group.
His timesheets, from BCG, show he worked on a number of projects including "industry structure" from October 1997 to January 1999.
Hooton refused to apologise.
He doesn't want to get into a prolonged argument with Cunliffe, but said: "I just don't think that doing a paper on research and development in the dairy industry can be described as helping with the formation of Fonterra.
"He obviously thinks that the paper he wrote ... was in some way crucial to the creation of the company but I don't think it would be a view shared by the industry leaders who lead the creation of Fonterra in 2000/2001."
Questions have also surfaced about Cunliffe's time at Harvard in the 1990s.
Cunliffe left the foreign service to pursue his studies after winning a coveted Fulbright Scholarship.
Cunliffe said this morning that he spent some time studying at both departments.
"I hold a Masters in Public Administration from the Harvard Kennedy School," he explained.
"It's a flexible course, almost half of which was studied at the Harvard Business School, some at Harvard Law School, and some at the Kennedy School.
"To my knowledge, no CV that I've put out has claimed that I hold an MBA [Masters of Business Administration] from Harvard Business School. I've always said I hold an MPA from the Harvard Kennedy School, sometimes called the John F Kennedy School."
A biography posted on the Labour party website until recently said: "He was a Fulbright Scholar at Harvard University's John F Kennedy School of Government and Harvard Business School, where he graduated with a Master of Public Administration."
On Monday the website was refreshed. The biography now reads: "He held a Fulbright Scholarship at Harvard University's John F Kennedy School of Government in 1994-1995, earning a Master of Public Administration."
Cunliffe's curriculum vitae has come under scrutiny since Fairfax Media revealed part of his CV had been erased after a "mistake" involving volunteer work he claimed to have carried out for a homeless charity.
He asked for a reference to Auckland City Mission to be removed from the biography posted on Parliament's official website. He also claimed to be a member of the Waitakere Forest and Bird Protection Society, but a spokesman admitted this was not current.
Fairfax is awaiting a response from Harvard.
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