"The business of politics is communication, and deliberately doing what he did in my view is just not acceptable. He should explain to the people in Hokianga and Moerewa and elsewhere who can't speak Maori what his promises are to them - not doing what he did.
I know what his game is here and you guys can excuse it but it's just not acceptable."
Te Reo Maori has been an official language since 1985 and Parliament has translators to translate for both MPs and audiences of Parliament TV. However, Peters argued that left out broadcasts on radio.
Flavell later hit out at Peters for "anti-Māori rhetoric" following on from his call to abolish the Maori seats.
"Every chance he gets he puts the boot in. To accuse me of hiding behind my native tongue harks back to an age when Māori were actively discouraged from speaking te reo.
I thought we were living in the 21st Century - not the 19th Century," said Flavell.
"Winston and his Hobson's Pledge mates might wish we were living in the past but I've got news for them - we're not."
Hobson's Pledge is a group involving former Act leader Don Brash who has praised Peters' stance on separatism.
Maori Party co-leader Marama Fox also weighed in, saying the Maori language should be celebrated in Parliament.
"It is more backward-looking nonsense from New Zealand First which is intent on fostering division."
NZ First has proposed a binding referendum on the Maori seats and also opposes giving iwi special powers or positions on local councils.