Two dozen bookings for a public meeting with David Seymour in Dunedin had to be cancelled after being identified as "very likely" to be disruptive, Act New Zealand says.
The acting prime minister and Act New Zealand leader visited the city on Wednesday and spent the early part of his night speaking to members of the public at an RSVP-only event, organised by the party.
Held at Distinction Hotel, the event was advertised online as a "public meeting with David Seymour" for a "discussion about the issues we face".
However, the online event page noted Act reserved the right to refuse entry to the event.
Emails circulating on social media from Act said some RSVPs were unable to be accommodated due to high numbers and room capacity, its members being its "first priority".
About 100 demonstrators also gathered outside the hotel as part of a protest organised by the Dunedin branch of the International Socialists Organisation Aotearoa.

Despite "a noisy group outside protesting on a variety of issues", the meeting went well, they said.
"Prior to the meeting, we identified RSVPs from individuals we judged very likely to attempt to disrupt the meeting from inside.
"This is a fairly common occurrence at political events, so we cancelled those bookings.
"The goal of a public meeting is to ensure voices can be heard, and it wouldn’t be fair on attendees to allow a small group to shout down the rest."
All the RSVPs were vetted — the process of which could not be disclosed for security reasons — and a total of 25 were cancelled.
Attendance was also constrained by the size of the venue, and it understood some people who were looking forward to joining "in good faith" may have been disappointed to have their RSVPs cancelled, the spokesperson said.
"We can assure, however, that David will be back in Dunedin.
"As for the protesters, we support their right to free speech and hope it wasn’t too cold outside."