The Electoral Commission has listed the Engineering, Printing and Manufacturing Union as a third party under the Electoral Finance Act.
That's despite a High Court ruling in May which found the union was considered a person under the Electoral Finance Act.
The National Party had challenged the EPMU's legal status as a third party, which gives it the right to spend up to $120,000 on electioneering.
The matter was referred back to the commission to determine whether the union is involved in the running of the Labour Party, which it is affiliated to.
The union is the largest in the country.
In a decision, the Commission has listed the EPMU as a third party under the Electoral Finance Act.