The High Court has agreed with NZ First leader Winston Peters that the Electoral Commission failed to uphold the law when dealing with two complaints during the 2014 election.
Comments by the ACT Party and the Conservative Party were published before the two days leading into the election, but were still available on the internet when no political advertising is allowed.
The court said because the public could still access the material during the prohibited period, the law should have applied.
Mr Peters said the Electoral Commission's job was to prosecute when there was wrongdoing and it failed to do so.
But he would not take the matter to the police.