Lawyers acting for Pike River Coal have been attempting to sit in on police and Department of Labour interviews as part of the investigation into the mining disaster, says the miners' union.
The mining company says it wanted its lawyers present so employees would not have to be reinterviewed for the company's own inquiry, but adds that their presence is voluntary.
Engineering, Printing and Manufacturing Union national secretary Andrew Little says members wanted the union to represent them, not the company.
The union wants the Department of Labour to ban the lawyers.
Mr Little says the company's lawyers have been turning up to the interviews and insisting on sitting in.
He says tempers flared when the company lawyers were denied access. He also says they badgered employees after the interviews.
Pike River Coal chairman John Dow says the lawyers' presence is voluntary and he believes any so-called badgering after the interviews has been misrepresented.
Mr Dow says the union has also objected to the company's obtaining a recording of the interviews.