Concern has been raised that advertising e-cigarettes could attract non-smokers.
One company, NZ VAPOR, is part way through an advertising campaign on an Auckland radio station.
Director of Auckland University's National Institute of Health Innovation Chris Bullen researches e-cigarettes.
He said although advertising the products could mean more people tried to quit smoking, there was concern it could also have the reverse effect.
"The advertising, if it's portrayed in a particular way, could be a means of recruiting non-smokers.
"There's a worry from some quarters that this could then lead on to actually smoking tobacco cigarettes and sort of glamourising the behaviour, and maybe recruiting a whole generation of nicotine-dependent young people."
Professor Bullen, who is also a member of End Smoking New Zealand, said it sounded like the NZ VAPOR ad was aimed at young adults.
"Having listened to the ad, I'm not persuaded that it's promoting e-cigarette use among very young people but it is youth orientated, (...) probably youths who go to bars."
But NZ VAPOR managing director QJ Satchell said their target audience was 35- to 55-year-olds, not young people.
"There's key things that are set around the website so people can't be under age and buying. And if we were to see that happening, we would certainly close their account."
According to the Ministry of Health, no e-cigarettes have been approved for sale in New Zealand.
Although it is illegal to sell e-cigarettes containing nicotine, people can buy the nicotine cartridges for the devices online.
NZ VAPOR said the adverts were pre-approved by the Advertising Standards Authority.
The Authority's chief executive Hilary Souter said ads were assessed as to whether they were socially responsible.
There were complaints about a television ad for e-cigarettes in 2013, but they were overruled.
"We've had a couple of previous complaints around a television ad, which had a very strong message around how bad tobacco smoking was.
"The approach this particular product took, the issues raised were around the timing of the advertisement and whether or not the advertisement was normalising the act of smoking."
Ms Souter said their approach was not about the legality of the products as such, but whether the adverts follow the Authority's codes.