Labour's primary industries spokesperson, Damien O'Connor, has asked Parliament's Commerce Select Committee to review allegations of market irregularities involving trading in Fonterra shareholder fund shares.
A complaint was originally made to the NZX, which did its own investigation and found no issue or any need to refer the matter to the Financial Markets Authority.
Mr O'Connor says the NZX's response was glib and shallow. He says the whole system needs to be looked at, because if units are going to be traded it's essential to know that it's being done in a fair, open and unmanipulated way.
He says the timing has been too "cute" and some of the investment managers monitor very closely what has been happening in the market.
"There's a pattern emerging that would indicate that some people are getting information and acting on it. Anywhere else it would be called insider trading and we need to check that out."
Fonterra declined to comment when approached by Radio New Zealand.