The Māori King should stay "above the ruck" of political affairs and remain neutral, New Zealand First leader Winston Peters says.
On Sunday, Kiingi Tuheitia made an unusually candid and political statement saying he backed the Māori Party and would no longer be voting for Labour.
Mr Peters said Kiingi Tuheitia should stay away from public support for political parties.
"When you head an organisation like that where there is a diverse group of political support, to ensure the allegiance of the group, staying neutral is very important.
"It will be of concern to a lot of Māori that this is happening, because they would expect him to remain above the ruck of what you might call tawdry political affairs," Mr Peters said.
Prime Minister Mr Key gave a tongue-in-cheek answer when asked what he thought of the comments.
"Yeah well we're in agreement on that one. None of us are going to vote Labour in the future," Mr Key said.
And while Mr Key was not so hot on the idea of the Mana and the Māori Party working together, he said he did not mind the Māori King not being politically neutral.
"Not if he keeps saying the first thing he said," Mr Key said.
The Labour Party was unfazed by the Māori King saying he would no longer vote for the party.
Its leader, Andrew Little, said Labour clearly had a very strong Māori backing, as it held six of the seven Māori seats.
"The king's comments are the matter for the king, but the Māori electors and the Māori electorates will make their decision on who they want representing them.
"The declining fortunes of the Māori Party reflect the fact that even though the Māori Party has signed up to the National party and government for the last eight years, it's not doing anything for Māori," he said.
However, the head of Māori studies at Victoria University, Maria Bargh, warned it could be unwise to completely dismiss the King's comments.
"Certainly there is a lot going on in the Kīngitanga and the Kauhanganui and that statement will influence people.
"It's not clear which way exactly they'll take it, but it is very meaningful that someone would speak so strongly," Dr Bargh said.