The minister in charge of road safety is unimpressed with a recommendation from her officials to introduce roadside saliva testing of motorists for drugs.
The ministry said drugged driving was a significant problem and that one in 13 drivers killed on the road have medications in their system that could have impaired their driving.
The number could be one in nine if recreational drugs were factored in, it said.
In its road safety briefing to the new government it said, while contentious, random roadside saliva testing would deter people from driving on drugs.
However, associate Transport Minister Julie-Anne Genter said there were major problems with the method.
"I have some concerns around the roadside saliva testing - it's extremely expensive, it's around $30 or $40 a test.
"We already have an extremely effective impairment test which is over 90 percent effective usually backed up by 100 percent accurate blood tests," Ms Genter said.
Police currently carry out a roadside impairment test on motorists they suspect are driving under the influence of drugs, where the driver carries out a series of coordination tests. If they fail the test they are then blood tested.
The proposed saliva testing would only test for recreational drugs and not medications that could be impairing motorists, and it would be intrusive too, she said.
"There are a whole lot of concerns around saliva testing so we've asked officials to come back to us with more advice on the options available in terms of making road safety more effective."
Blood test results in 2011 showed 94 percent of drivers who failed the roadside police impairment tests had drugs in their system.
However, Police Association spokesperson Chris Cahill said he did not think the current impairment tests were particularly effective and backed saliva testing.
"They really don't allow police to understand the true extent of the problem, or to deal with people who are impaired if they are not showing significant physical impairment which is not always the case."
'We don't think the technology has improved'
Drug Foundation executive director Ross Bell said very few countries used saliva testing to test motorists because the technology was not good.
And he said the Transport Ministry knew that.
"These were the same officials that gave advice to the previous National government that saliva testing technology was not up to scratch and we shouldn't do it in New Zealand.
"So I'm surpassed to see they're now saying it is up to scratch, because we don't think the technology has improved."
When in government, National also refused to introduce saliva testing - saying the devices used were not reliable enough or fast enough to be effective.
But the party's police spokesperson, Chris Bishop, said the party was now in favour, and he would not have a problem being saliva tested himself.
"As someone who doesn't use cannabis or methamphetamine I would feel comfortable doing that and I actually think it is the logical extension of roadside breath testing."
The Transport Ministry also wants the police to carry out more alcohol breath tests.
In 2016, police conducted 1.9 million breath tests - the lowest number in nearly a decade - down nearly 40 percent on 2013.