Pharmac has decided to contract a sole supplier for the blood sugar meters diabetics use and opposition parties say it will force an unwelcome change on thousands of people.
The drug-buying agency is going to get the meters from Korean supplier CareSens, and it will be the only type that is subsidised.
At present it buys meters from several manufacturers and Pharmac says the move will save $10 million a year.
It will use $4 million of that to subsidise insulin pumps, which will be funded nationwide for the first time.
CareSens is going to deliver three types of meters with enhanced features and Pharmac says it has responded to user feedback.
Labour's health spokeswoman, Maryan Street, says the change will be a disaster.
"It will mean thousands of people will have to switch to new glucose blood meters, disrupting their current management of what can be a life-threatening illness," she said on Wednesday.
"When consultation meetings were held around the country - at short notice and inconveniently - those people able to attend were furious and bewildered at why something which wasn't broken needed to be fixed."
NZ First's health spokeswoman, Barbara Stewart, says hundreds of thousands of diabetics will have to rely on "unknown" meters.
"The government and Pharmac care more about money than they do about people," she said.
"We've spoken with doctors, health professionals and diabetics and they all say this is purely an economic exercise aimed at saving a few dollars rather than doing what is best for those New Zealanders suffering from diabetes."
There about 150,000 registered diabetics in New Zealand.