The Advertising Standards Authority has ruled a Super City advertisement placed by the Greater Wellington Regional Council (GWRC) was "misleading" and "likely to exploit" the reader.
The authority has partly upheld a complaint from the Hutt City Council against the regional council, finding that five statements made in an advertisement placed in The Hutt News had "not been prepared with a due sense of social responsibility".
The board ruled that in certain statements the regional council had presented its own assumptions and opinions as facts, which was likely to exploit the "lack of knowledge of the reader".
It also found the regional council had misrepresented and misquoted the commission's draft proposal.
However, the authority ruled three other statements listed in the complaint were not in breach of its code of ethics.
In a statement released late last week, Hutt City Council chief executive Tony Stallinger said the public deserved explanations and evidence, not made-up facts.
"The campaign for a Super City is a shambolic con.
"GWRC has overstepped the boundaries of democracy - it has tried to fool the public into supporting a Super City. The Advertising Standards Authority's ruling confirms this."
He was also relieved the authority found it was incorrect to say Wellington local boards would have greater powers than Auckland local boards, Mr Stallinger said.
GWRC chairwoman Fran Wilde said the regional council did not believe it had misrepresented the Local Government Commission's report.
"GWRC believes our summary accurately portrayed the case for change described in great detail in the Local Government Commission's draft proposal.
"Each part of our region will struggle in the future to pay for upgrades to water and wastewater infrastructure and to roads. These are real issues and they were highlighted in the advertisement. We should be openly discussing these issues as a community, not shying away from them because they are difficult.
"We believe this sort of legal nit-picking by Hutt City Council is wasting ratepayer money and distracting us from addressing how we can ensure a sustainable future for the region."
The council was considering appealing the ruling, she said.
The deadline for submissions on the draft proposal to amalgamate the nine Wellington councils is March 2.