The Food Safety Authority has asked the Happy Valley Dairy company to recall milk manufactured around 15 October after some tested positive for E.coli bacteria.
Happy Valley Milk is distributed throughout southern part of the South Island.
The authority's director of compliance and investigation, Geoff Allen, says Happy Valley's own tests found the bacteria and it informed the FSA.
Mr Allen says samples contained high levels of E.coli which can cause gastroenteritis.
He says the authority is also investigating other products made by Happy Valley, which is not processing milk while the source of the bacteria is found.