Saturday night's New Zealand First victory in Northland is an opportunity for other provinces to ask, "What about us?" says Tauranga-based New Zealand First list MP Clayton Mitchell.
However, National's Tauranga MP Simon Bridges is "not worried" and is confident about progress.
NZ First leader Winston Peters won the Northland byelection with a majority of 4012 votes - a massive turnaround from National's 9000 majority just six months ago.
The final election night count gave Mr Peters 15,359 votes to 11,347 for National's Mark Osborne. Mr Mitchell said the victory was an historic moment.
"In 1964 there was a byelection where there was a complete changeover too - something like this hasn't happened since then and it's a really crucial time."
Mr Mitchell, who had spent weeks on the campaign trail with Mr Peters with just a few nights at home in Tauranga with his family, said other parts of New Zealand like Northland had been suffering under National's leadership for years.
"They had been forgotten and this is an opportunity for rural and provincial parts of New Zealand to stand up and say, 'What about us?'.
"It will certainly get other people asking the question, 'What has National been doing?'" He was unsure whether Saturday's byelection would rattle a traditionally blue stronghold in Tauranga, he said.
"But there are a lot of disgruntled people across all political spectrums in the Bay of Plenty and Tauranga specifically, with the same attitude toward National - what have they actually done?
"They say we have the TEL but what else? There hasn't been a lot done - and development in Tauranga - certainly not in recent years."
Mr Mitchell said the campaign was about sending National a message.
"Message sent," he said.
National MP Simon Bridges congratulated Mr Peters on his win. "Winston was a very effective campaigner and Northland was unique in terms of its circumstance - with the poverty and issues it has had for a very long time," he said.
"There is no question this will strengthen National's resolve to really achieve for the region and continue to be really visible to improve regional infrastructure and prosperity. We will make sure we continue to listen, where we can acting on what we are hearing and thirdly really demonstrate the progress we are achieving."
The byelection results were no way a sign of National's diminishing popularity, he said.
He was "not worried" about his position in Tauranga.
"We are really working hard to get progress on things that I know people care about such as schools, roading, broadband, healthcare."