NZX, the stock market operator, shows no signs of backing down in its dispute with the former owners of the Clear Grain Exchange, with a legal bill set to reach $4 million even before the case is heard in 2016.

The Wellington-based company expects to spend a minimum $1 million on legal fees related to the dispute this calendar year, adding to the $3 million already spent on lawyers in the dispute with Clear's former owners, Grant Thomas and Dominic Pym, and their companies Ralec Commodities and Ralec Interactive. NZX claims Ralec misled it with "wildly inaccurate" forecasts when the stock market operator purchased the grain exchange in 2009 for A$6.9 million upfront and potential earn-outs of A$7 million.

Ralec counter-claimed for sums totalling A$41 million, saying the stock market operator deprived it of the opportunity of earning the additional payments, and adding former chief executive Mark Weldon to the lawsuit.

"NZX continues to maintain its position that there is no substance to the claims made by Ralec and looks forward to having these legacy matters resolved through the courts," a spokeswoman said in an emailed statement.

The stock market operator hasn't made any provision to the litigation, but did write down the value of the Clear Grain Exchange by $2.4 million in calendar 2013 as trading revenues sank, and NZX decided to embark on a new operating model for the unit.

The grain exchange was set up to take advantage of the break-up of the Australian Wheat Board monopoly, and was looking to capture a slice of the A$100 million to A$150 million growers spent annually on commissions to sell their products.

NZX wanted to use the exchange to expand its agricultural products offering, and use it as the basis for an agri-portal for spot market and commodity data, though that hasn't eventuated due to Clear's muted trading volumes.

The dispute pre-dates much of NZX's existing management, hitting the courts in 2011, and both parties have been described as engaging in regrettable litigation tactics that have distracted from the main issues of the claims and counter-claims.

Last year, Justice Robert Dobson both parties were guilty of using "regrettable initiatives" that has caused the dispute to drag on, including "Ralec's attempt to generate anti-NZX media comment and NZX's attempt to warn Ralec shareholders off providing financial support for Ralec's counterclaim both fall into that category."

Last month, NZX chief executive Tim Bennett, who took over the reins at the stock market operator in 2012, said most of the costs to date related to discovery, which is largely completed, and the next phase of the case in preparing for trial will be at least $1 million.

Shares of NZX rose 1.8 percent to $1.16, and have decreased 2.6 percent this year.