The University of Otago has banned vaping, effective immediately, to the dismay of pro-cannabis protesters.

The tertiary institution has revised its smoke-free policy to include any electronic nicotine delivery systems, including vaporisers, "whether delivering nicotine or not".

That last point was squarely aimed at the three-times-a-week 4.20 protest by members of the pro-cannabis law reform student club, Otago Norml, spokesman Abe Gray claimed.

Hamish McNeilly/Fairfax NZ Abe Grey is angry the University of Otago is introducing a ban on vaping.

"The university doesn't want us to openly consume cannabis because they feel it is bad for their PR image with overseas students from conservative countries, so there is friction there".

Gray claims that when the university introduced the smoke-free ban in 2014, Vice-Chancellor Harlene Hayne told him that would be the end of the cannabis protests..

He responded: "We will use vaporisers like they do in every other modern jurisdiction where smoking is banned", something she warned him against, he said.

Those attending the 4.20 protest, which was held at that time on Mondays, Wednesdays, and Fridays, switched to vaporisers "in good faith".

Kevin Seales, University of Otago director of human resources, said the smoke-free policy was revised after the Vice-Chancellor's Advisory Group took public health advice.

"It was advised that the university should take a precautionary approach that excludes use of vaporisers on-campus and maintains all parts of the campus as smoke-free in the broadest sense, which is an approach taken by a number of other universities."

He said everyone on the campus was expected to abide by university's policies and the law.

Gray said the protest was in its 12th year and had survived not only the introduction of the smoking ban, but also undercover surveillance and arrests by police in 2008.

Police showed no more interest in the protest, unlike the university, he said.

"They want (the 4.20) gone."

If the club was forced out of the campus, members would protest outside the university's gift shop on Cumberland St, by the main one-way system.

"We will move it out there if we have to."

Drug Foundation director Ross Bell said if evidence showed vaping was safer than smoking a combustible product, "surely people should be encouraging the less risky mode of smoking".

"Would they ban nicotine patches? It would be disappointing if this was a backdoor way of shutting down protesters that they tried to shut down in the past ... it seems a little bit cynical."