The Maori Party is blaming the Electoral Commission for the fact that the number of Maori roll seats isn't going to increase for the next two elections.
It says the commission didn't try hard enough to explain the Maori option it conducted during the first half of this year.
Maori voters were given the choice of changing from the general roll to the Maori roll, or vice versa.
The results, announced in June, showed a nearly even split - 8859 switched to the Maori roll and 8261 switched to the general roll.
There were 6457 new voters on the Maori roll, but the increase was well short of the number needed to create another Maori electorate.
Statistics NZ factored in the latest census figures and said on Monday the Maori roll seats would stay at seven.
Maori Party co-leaders Tariana Turia and Te Ururoa Flavell say the commission didn't do enough to ensure people fully understood the difference between the rolls.
"The Electoral Commission spent around $1.5 million on the Maori option campaign but measured their success on the number of times the advertisements were viewed," they said.
"It didn't ensure the messages were received and were transformed into action - filling in the forms and sending them back."
Labour has blamed the Maori Party for the insufficient increase in the Maori roll.
It says the party's drawn-out leadership struggle, which took nearly a year to resolve, turned Maori voters off politics.