Norml, the self-proclaimed ''cannabis reform'' group, has reserved a university lecture theatre for the film's premiere today.
Prof Hayne's warning was added to a standard agreement used when groups host events in university lecture theatres.
The documentary, Druglawed, looks at the war on drugs in New Zealand, Australia, the Netherlands and the United States.
South African director Arik Reiss began filming Druglawed in Dunedin after meeting Norml member Abe Gray in 2009.
''I started researching the history of it ... and realised it was quite an important issue.''
The documentary follows several New Zealanders, including Mr Gray, Mr Reiss said.
''I don't think the film encourages illegal activity,'' he said.
''It shows civil disobedience happening, but it doesn't say `go out and do this'.''
