Fonterra has placed a halt on trading its shares after realising there "may be a variation from the earnings guidance previously given to the market".
The co-op was preparing statements for the financial year ended July 31 when it made the discovery.
"Fonterra is working to determine whether this is the case," Fonterra company secretary Anya Wicks said in a statement to the NZX.
Shares on the NZX, the Australian ASX and the Fonterra Shareholders Market are all affected.
Fonterra says it should have new earnings guidance figures by August 10.
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Shares are currently worth $5.11, down from $6.68 in January.