The National Party has failed in a bid to stop the Labour Party-affiliated Engineering, Printing and Manufacturing Union from campaigning in this year's election.
The Electoral Commission has decided to list the Engineering, Printing and Manufacturing Union as a third party under the Electoral Finance Act, along with a number of other unions.
That means the union, the country's biggest, can spend up to $120,000 on electioneering.
It is the second time the Electoral Commission has ruled the Engineering, Printing and Manufacturing Union is a third party.
The first decision was overturned by the High Court after an application from National.
The matter was referred back to the commission to determine whether the union is involved in the running of the Labour Party.
National deputy leader Bill English says the party accepts the ruling, but says the whole question of electoral finance law needs to be looked at by the next Parliament.