The Electoral Commission is to hire a firm to begin surveillance of political advertising from January 1.
And it says it will refer breaches of the Government's new election spending law to the police.
The watch-list will include Invercargill Mayor Tim Shadbolt's tertiary funding campaign.
Commission chief executive Helen Catt yesterday said the commission would actively monitor ads.
This follows the passing of the Electoral Finance Bill yesterday.
"What the legislation is saying is that the election campaign starts on the first of January," Dr Catt said.
"From that point on, it is the election campaign."
The Herald understands that several groups are planning political advertising campaigns almost immediately that will challenge the new law.
During yesterday's third reading of the bill, United Future dramatically changed sides to oppose it.
Leader Peter Dunne said New Zealanders had gone past caring about the bill's content.
"They simply mistrust it," he said.
It was seen not so much as an attempt to resolve problems, but as a case of "political utu".
"Legislation perceived in that way cannot succeed."
The passing of the bill marks a milestone in the battle over Labour's spending of public money on its pledge card before the 2005 election and National's role at the same time in encouraging a covert campaign of support by members of the Exclusive Brethren church.
The bill imposes new restrictions on political advertising by people and groups outside Parliament.
Anyone spending more than $12,000 must register, and no registered third party is allowed to spend more than $120,000.
But MPs are exempt, and registered political parties can spend up to $2.4 million.
The bill passed 63 votes to 57, with the support of Labour, the Progressives, New Zealand First and the Greens. Independent MP Gordon Copeland, who opposed the bill, was overseas and did not vote.
National Party leader John Key received a standing ovation for his hard-hitting speech from colleagues and many in the public galleries, including from Mr Shadbolt, who has threatened to test the bill early in the New Year over the Southern Institute of Technology funding.
"This is a sad day for New Zealand," Mr Key said.
"It is the day the Labour Party admitted publicly and through legislation that it can't win unless it changes the law."
Prime Minister Helen Clark, her deputy, Michael Cullen, and Labour's No 3 minister, Phil Goff, were not in Parliament during the debate.
But earlier, during question time, the Southern Institute of Technology gave Mr Key an example of what the bill could restrict as he repeatedly challenged the Prime Minister.
Helen Clark said that if Mr Shadbolt stuck to the issue - and by implication did not criticise the Government - his advertising campaign would be within the law.
"He can spend as much as he likes on issues advertising," she said.
Maori Party MP Hone Harawira attacked Labour's motives on the bill, which was not, he said, about election finances.
"It's about the sweet scent of power, and the lust for control. It's about the decadence of corruption, the stench of deceit and the refusal to accept the reality of impending defeat."
Justice Minister Annette King and Progressives leader Jim Anderton attacked the Herald for its campaign against the bill, suggesting it was motivated by money rather than freedom of expression considerations.
Ms King said the bill did not restrict free speech.
"It restricts the right to purchase speech through advertising. This has been done to safeguard our democracy by keeping to a minimum the undue influence of money in politics."
Dr Catt last night clarified the Electoral Commission's view on how it would interpret advertising material from January 1, saying it would not be "time nuanced".
That rejected the view expressed in the Herald yesterday by the Coalition for Open Government, which suggested that advertising published in January would be treated differently from the same advertising published a week before an election.
She said all advertising would be treated the same from January 1, which was the date from which the election campaign started.
The commission yesterday held a meeting in Wellington for about 30 officials of political parties, including National, to discuss the new law.