During the second reading of the Arms Legislation Bill in February, NZ First MP Ron Mark said the caucus had some reservations about the bill.

The Labour party is struggling to get support to pass a new gun law as NZ First continues to dig its heels in.

The Arms Legislation Bill passed its second reading last month but NZ First MP Ron Mark signalled the party was moving away from supporting core aspects of the Bill, saying the caucus had some reservations.

While he would not go into detail, Mark told Stuff this week there was still "a lot of water to go under the bridge right now".

THOMAS COUGHLAN/STUFF NZ First leader Winston Peters told gun protesters outside the NZ First party conference in Christchurch, in October, that the party was going into the gun law process with open ears.

The bill, which includes a firearms registry, harsher penalties, and a warning system to show if a person is a fit and proper person to hold a firearms licence, had been expected to come back to Parliament this week but has been bumped down the order list.

It is unclear how long it may take but the bill is not expected to pass before the first anniversary of the Christchurch shooting on March 15, which had been the Government's initial preference.

ROBERT KITCHIN/STUFF Police Minister Stuart Nash said the three parties in government were working constructively on the Bill. He was working on a Government amendment to incorporate more than 25 changes as a result of the Select Committee process.

Mark said he was still having "constructive conversations' with Police Minister Stuart Nash on the issues the party wanted to settle.

The party was looking for a pragmatic way through that protected the rights and privileges of legitimate firearms owners, he told the House last month.

One of those was resolving the question of whether or not police should continue to administer firearms law and a "strong argument" for the need for an arms authority that takes that statutory responsibility.

There were also further conversations to be had around farmers who had problems with pest control and around sporting shooters.

Meanwhile, Green Party Justice spokeswoman Golriz Ghahraman said the party supported the "long overdue" legislation would will ensure New Zealanders felt safer when going about their daily lives.

"We have fought for a gun register and stricter tests for gun ownership for many years. We currently do not have any amendments but will work through amendments at committee stages."

NZ First may choose to join the National Party and the ACT Party by putting up amendments to the Bill during the committee of the whole House. However, it may instead continue negotiations with Nash, who is putting up a Government amendment.

When asked what his preference was, Mark said it depended on the outcome of the conversation with Nash.

It comes as the gun lobby puts pressure on the party to renege on its commitment to pass the laws, telling supporters NZ First would be "toast" in the election if it supported the new gun law.

New Zealand Police Association president Chris Cahill has urged "those who are the subject of lobbying" against the Bill, to question the veracity of petitions they are receiving.

"My concern is based on receiving two emails from the gun lobby group COLFO, confirming delivery of my letter to NZ First Leader Winston Peters urging him to reject the Arms Legislation Bill. Given I never sent such an email to Mr Peters and, for glaringly obvious reasons I never authorised COLFO to add my name to their campaign, I wonder how many others are in the same position?"

Firearms owners who took part in the buy-back have stepped up and now it was time for their elected representatives to do likewise, he said. The Bill needed to be passed into law and a firearms registry is a must, he said.

Nash said there was still some material to sort through in detail and he was having ongoing conversations with representatives of the Green Party and New Zealand First on next steps for the Bill.

"I am open to amendments during the Committee stage of the debate, if they meet the overall objective of the Bill. That is to keep people safe, stop firearms falling into the wrong hands, and restrict ownership to responsible licensed people."

The Government was committed to increasing the penalties for gun crime, prevent gang members ever getting a firearms licence, and establishing a firearms register to better track firearms through the community, he said.

The three parties in government were working constructively "For example, I am working on a Government Supplementary Order Paper to incorporate more than 25 amendments as a result of changes recommended by the Select Committee, following public submissions."

The Select Committee process resulted in a number of changes to the Bill that included: the duration of a firearms licence remaining at 10 years, new restrictions to prohibit carbine conversion kits for pistols, modified language around health considerations and the clarification of privacy issues around access to the register by agencies like NZ Customs and the Ministry of Foreign Affairs and Trade.

Australian firearms control expert associate professor Philip Alpers, who spoke to Stuff when visiting Wellington last week, said the gun lobby had "got its teeth back into the political system" after falling quite following the March 15 terror attacks.

"It has largely watered down some of the provisions of the registration system," he said, citing the select committee's decision to mostly maintain 10-year licencing periods.

He said the NZ First MPs reconsidering their support of the legislation needed to "get real".

"Here you have a tiny minority of dedicated, who call themselves single issue voters, who are terrifying politicians by convincing them that they are much more numerous and much more powerful than they could possibly be."