The union representing West Coast miners say it is "totally unacceptable" former Pike River Coal chief executive Gordon Ward is refusing to appear before the Royal Commission of Inquiry into the disaster.
The comment comes after the Pike River Coal board chairman John Dow yesterday told the Commission Mr Ward left the company after falling out with his board over performance problems.
Mr Dow said he had been asked to step in as a mentor to Mr Ward in 2010, however a review of Mr Ward's performance found multiple problems went unresolved until August last year, he said.
"I couldn't... for the life of me understand why it was so important for Mr Ward to keep assessing at the optimistic end.
"Mr Ward subsequently left Pike River Coal."
Mr Dow said when he signed on as board chairman, he understood the mine was Mr Ward's "baby".
Engineering, Print and Manufacturing Union assistant national secretary, Ged O'Connell, said Mr Ward played an integral role in the development and running of the mine.
He said Mr Ward could provide crucial insights and evidence into the mine explosion.
"When you have Pike chairman John Dow making numerous references to the high degree of involvement of Gordon Ward at the mine, it is inconceivable and totally unacceptable that he is not wanting to appear," Mr O'Connell said.
"No only could Ward shed light on what happened, but his evidence could help prevent another tragedy.
"If nothing else, he owes it to the memory of the men who died at Pike."
The Royal Commission cannot compel people who reside overseas to appear before it.
Mr Ward is understood to be in Australia.
"We need to remind Mr Ward that corporate responsibility is an issue with this disaster.
"He led the company right up to a few weeks before the explosion. If the current legislation can't compel him to appear before the commission then the law should be changed," Mr O'Connell said.