Foreign Minister Murray McCully has suspended the funding New Zealand provides to Nauru each year for its justice system because of ongoing concerns about civil rights abuses.
New Zealand had been giving Nauru $1.2 million a year, paid quarterly.
Mr McCully said several incidents had caused him concern, including the removal of senior members of the judiciary.
Earlier this year, five opposition MPs were expelled from parliament for more than a year, with three now facing criminal charges after a protest outside Parliament in June, while another has had his passport suspended.
There has also been widespread criticism of new laws that restrict freedom of expression and assembly, as well as restrictions on internet access and social media.
Mr McCully said the issues with the justice sector and human rights in Nauru had been under discussion for a number of months now.
"We've just not been able to successfully resolve the differences that exist on that matter."
He had previously met with the Justice Minister and other ministers from Nauru, and said he had received assurances they intended to remedy the problems and restore international confidence.
"We agreed to go forward with our funding on that basis. Now I've reminded them of the obligation that they entered into with us at that time.
"I've made it clear that some of the actions that have taken place recently we regard as being incompatible with those assurances."
Roland Kun case raised
One relates to the case of MP Roland Kun, who has had his passport taken from him by the Minister of Justice. The MP's wife and family live in New Zealand and he has been unable to return to them.
"And I pointed out that we in New Zealand have a system where judges can take passports off people if they're before the court and if they believe they're a flight risk but to have the action taken by a political opponent and where there are no charges laid against the individual concerned gets into territory we're not comfortable with," Mr McCully said.
"I've made it clear we are very reluctant to take our funding away, we're reluctant to even to even place it on hold but where the system that we're funding is essentially part of the problem rather than the solution, we don't have much choice."
Mr Kun said it was disappointing that New Zealand had been forced to suspend aid but that it was inevitable given the Nauru Government's failure to respond to New Zealand's concerns.
"New Zealand is the biggest donor partner who is assisting us with the strengthening of our justice system here on Nauru, so New Zealand does have great interest in what is happening in the justice sector.
"That the government of Nauru has failed to satisfy New Zealand in terms of the pursuit of their shared objectives of strengthening the justice sector on Nauru is very disappointing."
Mr McCully said the ball was in Nauru's court, and he would continue to work with its government, with the aim of reaching a point where the funding could be resumed.
But Nauru's government said the decision was misguided and based on misinformation from the opposition MP Roland Kun.
It said Mr Kun was being investigated for his part in instigating a riot at the country's Parliament House, which it said was a potential act of treason.
New Zealand's actions sought to undermine Nauru's sovereignty and influence a criminal investigation, it said in a statement.
New Zealand applauded
Nauru's former chief justice, Australian Geoffrey Eames, was forced to resign from his position in January last year after the Nauruan Government cancelled his visa.
He told Checkpoint New Zealand's move sent a strong message to Nauru that the rule of law mattered.
"The fact of the matter is the message will get across by this action but it is a serious event and they can't simply dismiss it and pass it off to the local people in Nauru as if it's merely a matter of an attack sovereignty," he said.
Mr Eames said Australia continued to turn a blind eye to abuses of power in the Pacific nation.
New Zealand Law Society spokesman Austin Forbes said it was reassuring the Government was prepared to take action, and that it sent a clear message to the government of Nauru.
The Labour Party has also backed the move with Labour Foreign Affairs spokesperson David Shearer saying it was the right thing to do.
Mr Shearer said while Australia had a different relationship with Nauru, he expected it to be putting pressure on the Nauru government to improve its civil and human rights record.