NRU chief executive Jeremy Parkinson said the signs were not intended to upset or promote anybody other than tomorrow's game and were meant as a tongue-in-cheek response to the election signs that were springing up around the country.
As well as Labour complaining, Mr Parkinson said the National Party had also expressed unhappiness at the billboards and the union apologised for any upset caused by the signs.
But Whangarei Labour candidate Kelly Ellis said she did not believe they were a parody and that several members of the NRU were also National Party members, so should have known of the potential conflict with the act.
"Pull the other one, it plays Jingle Bells," Ms Ellis said when hearing that the signs were meant to be a joke. "They are damn cheeky and underhand. We are trying to run a positive campaign while this sort of thing just cheats the rules and is a blatant attempt to promote National."
However, Mr Parkinson said the signs were created by the NRU's commercial manager Alistair McGinn and had no input from the NRU board, the National Party or any National Party MPs or members.
"We did not even think that it would breach the act and it was never our intention to promote anybody or anything, other than tomorrow's game. We will learn from this and Alistair has been spoken to, so this won't happen again. But all publicity is good publicity for the game tomorrow."