The Green Party won't accept a Labour-New Zealand First coalition that doesn't involve them and it's a position that could force voters back to the polls, the party's newest MP says.

Barry Coates says his party will be the "beating heart" of the next government come September, so won't get behind a National-New Zealand First government either.

In a post for the Daily Blog Mr Coates wrote the Labour-Green memorandum of understanding, signed last year, was the foundation for building the next government.

It is a commitment to work together to change the government.

"However, if we were not part of a coalition, we would not accept a Labour-New Zealand First government and certainly not a National-New Zealand First government," he said.

"Neither will be acceptable to the Greens."

He told Newshub it could mean making voters to go back to the polls.

His blog comments were echoes of a similar statement made by Green Party co- leader Metiria Turei at the party's campaign launch over the weekend.

In the same speech she labelled NZ First leader Winston Peters racist.

Both the Green Party and New Zealand First were polling at 11 per cent, according to the latest TVNZ-Colmar Brunton figures, released this week.

Mr Coates was elected to Parliament in October last year to replace Kevin Hague, who took up a position heading Forest and Bird.