Shares in the NZX have fallen 4% following a newspaper report that a legal stoush over the purchase of the Clear Grain Exchange could cost the stock market operator millions of dollars.
NZX's shares fell 10 cents to $2.40 each.
The Dominion Post reported NZX is suing the former owners for deception when it sold the Melbourne-based exchange in 2009.
Grant Thomas, one of the lawyers for one of the owners, called the suit frivolous and unfounded.
Rob McGirr warns his client is ready to file legal action against NZX and seek up to $17 million in performance targets under the contract.
NZX responded on Friday, saying Mr McGirr's comments are inaccurate, and the amount of grain traded on the exchange has not met the agreed targets.