ONE News investigations have uncovered concerns about a possible conflict of interest for the Minister of Building and Construction, Maurice Williamson.
And it is prompting calls from the opposition for Williamson to step aside from any Government decisions over the Mainzeal collapse.
Williamson helps oversee New Zealand's building industry and he has been commenting on sub-contractors being left out of pocket in the Mainzeal collapse.
But Labour says he should be nowhere near the matter.
"There are legitimate issues for sub-contractors, but the problem here is that Maurice Williamson has a conflict of interest," said Grant Robertson, Labour deputy leader.
Holyoake Industries, owned by rich-lister Noel Holyoake, is a large supplier of air conditioning and ventilation systems.
On its website it lists the Mainzeal-built Supreme Court in Wellington as one of the projects it has been involved with.
No one from Holyoake Industries would appear on ONE News today, however staff confirmed that they do have direct dealings with Mainzeal, and supply to a number of firms who work with Mainzeal.
They also confirmed that Williamson is still a director after joining the board in 2003.
"He's the director of a company that is intimately involved with Mainzeal. He's a minister making decisions. He needs to step aside," Robertson said.
Williamson does not feature among the listed directors on Holyoake Industries' website.
However, he was given approval by the Prime Minister to be on Holyoake's board.
Williamson has disclosed his directorship to Parliament.
He has also declared Mainzeal's gift of corporate box hospitality at a Rugby World Cup semi-final.
Williamson would not be interviewed but issued a statement to ONE News.
"On becoming a Minister, I instructed officials that I would not receive papers on and would withdraw from discussions about heating and ventilation because of my directorship of Holyoake Industries Ltd," he said.
"I will continue to deal with issues related to Mainzeal, where that does not conflict with my declared personal interest."
Business commentator Brian Gaynor says ministers should not be on boards of major companies.
"If somebody is a minister or involved in the Government in a major way, they should not be on the board of a major company, particularly if that company is involved in the industry in which the minister is directly involved in," Gaynor said.
Labour says the pressure is now on the Prime Minister to explain why Williamson has been allowed to stay on as a director.
ONE News political editor Corin Dann says the issue of ex-politicians being on company boards has well and truly been thrust into the limelight with Dame Jenny Shipley having resigned as as chair of the Mainzeal Group.
Questions are now being asked about whether serving ministers should be on boards, he said.
Dann said there is no suggestion that Williamson has done anything wrong.
"We're talking about the perceived conflict of interest here. And I guess there's some level of trust that he's able to make that judgement call on whether or not he can comment on a Mainzeal issue," Dann said.
"Now obviously the opposition are not particularly happy about that," Dann said, adding "it is a pretty messy look."
He said he thinks we can expect to see "a lot more heat" on the Minister tomorrow when Parliament resumes.