Christopher Luxon explains why National is joining the Greens with criticism of controversial Mass Arrivals Bill

"When you've got the National Party and the Greens agreeing on it, that just says a lot."

That's the message from National leader Christopher Luxon, who's in lock-step with a party at the other end of the political spectrum in opposing the Government's Immigration (Mass Arrivals) Amendment Bill.

The Government is currently trying to pass the bill into law. The law would enable 28-day warrantless detention of asylum seekers, up from four. 

Luxon said National doesn't agree with the new legislation.

"Again, it's a classic Labour Government thing, isn't it? I mean, we're 70 days out from an election, it's a solution or an ideology roaming around in search of a problem to attach to and we just don't see the need for it," he told AM host Ryan Bridge.

"We think there's enough protection under existing provisions, the public submissions that were held on this bill through the Select Committee process were very strongly against it and you've actually seen a number of political parties come out in opposition to it."

It "says a lot" when the National and Green parties were aligned on issues, Luxon said.

He believed the Greens were right to oppose the bill, saying the legislation wasn't needed or necessary.

"I sit on the Intelligence Committee and so I am aware of intelligence issues and security issues in New Zealand but… this bill for us, in our assessment of it, makes no sense - it's the wrong time to be doing it 70 days out from an election. More importantly, the existing provisions will give us enough protection and, as I've said, you've seen public submissions united against it and you've seen political parties here in Parliament against it."

Green Party immigration spokesperson Golriz Ghahraman said she was "shocked at the refusal" from the Government to engage with "every expert and community group, not to mention genuinely concerned individuals" on the legislation.

During the legislation's first reading in March, Ghahraman said the bill highlighted "a sad day for our nation". 

"It is the first time that a political party - certainly a Government - has made the humanity and the rights of asylum seekers an election-year issue. It certainly doesn't seem like detaining asylum seekers without charge or trial would be a bread-and-butter issue for a Labour Government, but here we are," she said, referring to Chris Hipkins' pledge to focus on "bread and butter" issues when he took over as Prime Minister earlier this year.

"So, at best, this bill is an unnecessary waste of this House's time; at worst, it's breathtakingly reckless. But we will continue to stand with our communities as this bill and their humanity gets debated," Ghahraman said.

Little, however, has accused other political parties of being "wilfully blind" - saying the legislation was on the back of up-to-date risk assessments.

Ghahraman, meanwhile, said Little should "go back to the drawing board".