The anonymous photograph "postcards" were sent to some Dunedin city councillors, Community Trust of Otago staff and trustees and sections of the media yesterday.
The Otago Daily Times received three, including one that read: "Surveys show the public support it. Yeah right".
The compilation images appeared to be homemade, using photographs of actual Tui billboards with fridge magnets placed on top.
Stop the Stadium president Bev Butler denied any knowledge or involvement in the campaign, but said it sounded like "quite a good thing for people to be doing".
"It's harmless isn't it?" she said when contacted yesterday.
Tui brand manager Jarrod Bear, of Auckland, disagreed.
He was unaware of the campaign until contacted yesterday, but said the company would be prepared to take action to protect its brand from unauthorised use.
That could begin with an approach being made to the author, if identified, but in a "worst-case scenario" the matter could end up in court, he said.
Tui - owned by DB Breweries - occasionally granted permission for others to use its brand.
However, Mr Bear said in this case the company was "not aware of it, and definitely wouldn't sign off on it being used for those purposes".
"If we can find out who is doing it, we would definitely look to protect our intellectual property," he said.
The release of the anti-stadium material comes just days before this weekend's planned anti-stadium march, being organised by Stop the Stadium, and ahead of the council's scheduled vote on the $188 million stadium on February 9.
Earlier this week, Ms Butler also confirmed the group was considering organising a "rates revolt" for those opposed to the project, due to the council's "arrogance that must soon push people into more radical modes of opposition".
Yesterday, she said she had heard of other anti-stadium acts around the city, including stencilled "no stadium" slogans spray-painted on footpaths and a white elephant on a wall.
"This is, I guess, what can happen, especially when so many people are opposed [to the stadium].
"Other people just spontaneously start doing things," she said.
Community Trust of Otago chief executive Keith Ellwood, whose organisation is considering an application for $10 million in stadium funding from the Dunedin City Council, said at least one trustee and a staff member had received the postcards.
Asked if he knew who was responsible, Mr Ellwood said "probably". He would not elaborate.
"I doubt it will have an impact on the decision-making process of the trust," he said.
