The Maori Party says the independent MP, Hone Harawira, has breached their agreement by announcing he plans to call a by-election.
Mr Harawira's agreement with the Maori Party allows him to stand, uncontested, as an independent MP in Te Tai Tokerau electorate.
In return, he agreed not to stand candidates against his former colleagues if he formed a new party.
On Saturday, Mr Harawira announced the formation of his new left wing party, the Mana Party, and also that he plans to force a by-election in his Te Tai Tokerau electorate.
Maori Party president Pem Bird says he and other party members were shocked by the by-election announcement.
He says Mr Harawira's actions mean the Maori Party is not duty bound to honour the agreement.
Mr Bird says a Sunday night meeting of the party's council will determine whether it will stand a candidate in Te Tai Tokerau electorate.
He says suggestions the Maori Party had already approached candidates in the Far North, were incorrect.