Prime minister John Key today announced plans for a referendum on the issue within the next three years.
His opponents said they would hold to those plans even if they oust Mr Key and his National Party in elections later this year.
The NZ flag depicts the Southern Cross constellation and includes the Union flag in the top left corner.
Many critics say it is too similar to Australia’s flag and fails to reflect New Zealand’s independence and status as a former British colony. Former military personnel are at the forefront of opposing the move, while advocates do not agree on what the new flag should look like.
Mr Key favours a silver fern set against an all-black background, an image popular among NZ sports teams. Some say that would equate New Zealand too much with its sporting heroes and would be too reminiscent of a pirate ensign. Some argue the indigenous Maori should be represented in any new flag.
In a speech, Mr Key said: “The flag remains dominated by the Union Jack [sic] in a way we ourselves are no longer dominated by the United Kingdom.”
He said Canada’s 1965 decision to embrace a maple leaf design was a good example, and he couldn’t imagine Canadians now wanting their old Union flag back.
“We should be represented by a flag that is distinctly New Zealand’s,” said Mr Key, adding it would not signify an ending of constitutional ties to the British monarchy or participation in the Commonwealth.
“We retain a strong and important constitutional link to the monarchy and I get no sense of any groundswell of support to let that go,” he said.
One poll late last month showed only 28 per cent of respondents wanted to change the flag, with 72 per cent happy with the current version.
Representatives of service personnel have argued that troops have fought and died under the existing flag.
Don McIver, president of the Returned and Services Association (RSA), said: “The view of the RSA is there is no need to change the flag.
“Thirty-two thousand New Zealanders have given their lives under the flag and many more thousands have served under it in a combat environment.”
The Republican Movement of New Zealand, which advocates an end to recognising the British monarch as New Zealand’s head of state, remains indifferent.
“We realise there is momentum to change the flag, and are not against it,” said its chairman, who goes by the single name Savage. “But the substance is changing the head of state. It’s symbolic only to change the flag.”
Yet for many, a new flag would represent another small step by New Zealand toward disentangling itself from its colonial past.
Recent polls have yielded conflicting indications about whether a majority favours a change. Victor Gizzi, a sales manager at flag manufacturer Flagmakers, said “older people tend to want the status quo”, while younger people feel differently.
Mr Key, who on Monday called an election for 20 September, said the vote would be held within three years.
New Zealand will go to the polls in September so that a new government will be in place by the G20 meeting due to take place in Australia in mid-November. Mr Key’s party has a sizeable lead over the Labour opposition, latest polls show.