NZX is yet to say whether Fonterra complied with its continuous disclosure regime in the way it handled the botulism scandal.
Fonterra has acknowledged it knew deadly bacteria had contaminated some ingredients used in other products, including baby formula, last Wednesday.
However, it did not advise the stock exchange until Monday.
The news, which was announced on Saturday, sent both the Fonterra shares, which only dairy farmers can own, and Fonterra Shareholders' Fund units, which anybody can own, into a tailspin on Monday.
Both securities are listed on NZX.
NZX listing rules require all listed companies to disclose any material information immediately they become aware of such information.