Fellow resident Julia Banks is also refusing to buy anything from the store.
"We don't need kids exposed to this kind of thing. I think it's completely and utterly wrong to be sold in a dairy," she said.
Ms Banks hoped others would follow their lead and boycott their local store if it sold legal highs.
"To have this stuff freely available in dairies is disgusting.
"It's the sort of place you pop in to get your bread and milk. Not to get drugs."
Her husband, Warren Banks, said many people wanted to keep synthetic cannabis out of dairies.
Manurewa residents this month protested outside a High Zone store to protest the sale of the drugs in the community.
Matua Residents' Association chairman Richard Kluit said it had received at least 25 letters from residents supporting a proposed petition against the dairy's sale of synthetic cannabis.
Mr Kluit said the committee was yet to discuss what action would be taken, if any, but "things are heating up".
"At this point, I can't say 'hey, yes we are going to put it to the dairy'. I suspect we will because some of the feedback from the community is supportive of that but we also have to look at this as a legal operation and these people are trying to earn a living in our neighbourhood.
"Personally, I'm against it and I think [the objection] is a good thing but 25 households out of 2000-plus is not a major figure. We will need to get closer to 100 before we really know more."
Mr Kluit said the matter might be similar to community upset when AJ's Bar first opened in Matua "but 10 years later, there's been no issues with it".
Matua Dairy assistant manager Raj Singh said the dairy never used to sell legal highs but was now catering to demand. The number of people coming in for synthetic cannabis could be eight to 10 times a day, he said.
"It's a real controversial issue and it's difficult for us as well. If somebody comes in and wants it and I don't give it to them, they go somewhere else and I lose a potential customer.
"They buy other things as well . . . they buy munchie food."
Mr Singh said it appeared he would lose customers either way. "I'm not forcing somebody to smoke it. People come in and ask, so we supply."
Next month, a final report into a Psychoactive Substances Bill is expected to bring in legislation to regulate otherwise unregulated psychoactive substances such as party pills and legal highs such as synthetic cannabis.