Tricia Cheel, from WavesNZ, the organiser of the screening in Kaitaia, accused Dr O'Sullivan of threatening and disruptive behaviour and of "holding Kaitaia to ransom with his Government health funding for Moko".
Moko is the Manawa Ora Korokoro Ora (Moko) programme, Northland's first full-time, school-based health clinic, which Dr O'Sullivan founded.
Ms Cheel said other health professionals as well as the public relied on that initiative and did not want to cross Dr O'Sullivan.
She said he had been invited to watch the film with other health professionals, but he stood at the entrance discouraging people from coming in, then commandeered the stage.
"His behaviour was totally over the top," Ms Cheel said.
A video shows Dr O'Sullivan telling the audience: "I've come here not to watch the film, but to continue my battle and my challenge for my people ... and importantly, for our children.
"I come here with a lot of anger ... that's because I am adamantly opposed to this because this position is, this idea of anti-immunisation has killed children around the world and actually will continue to kill children whose parents are put off immunisation because of misinformation - misinformation based on lies.
"Fraudulent people for their own reasons have decided that they would put forward false information that actually causes harm to children.
Ms Cheel said Dr O'Sullivan did a haka before he spoke, pointed his finger at her and other people in a threatening way and appeared to shake with anger.
Ms Cheel made an incident report, but did not lay a complaint, with Kaitaia police over what she felt was initimidating and disruptive behaviour.
She said Vaxxed was not an anti-vaccine movie but was about "vaccine safety and scientific integrity".
However, she now refused to talk with "mainstream media" about the film unless the interviewer had watched it - "because media bias is so great", she said.
The film will be screened at the Otamatea Reportory Theatre, Maungaturoto, at 7pm tonight.