If people aren't being breath tested, they'll fall back into habits of not watching what they're drinking when they drive, National's police spokesman Chris Bishop says.
There has been a sharp decline in roadside breath tests, at the same time as the road toll climbs in New Zealand.
In 2013, there were 3 million breath tests completed, but last year the number had dropped to 1.4 million - less than half the total of five years earlier.
"I think Kiwis will be concerned about that [number]," Mr Bishop said. "People really do notice it and I think over time it does change people's behaviour because when people know that there's a chance they're going to be breath tested they do think about what they're drinking.
"At the moment it's basically impossible to get stopped because the police aren't doing the tests."
Police have said they are being more strategic, more targeted, using evidence and targeting high risk areas, which all sounded good, Mr Bishop said, but it was the areas which didn't show up as high risk, which people still drove home on after having a few drinks at work or the pub, which needed to be tested as well.
"If you don't test people then you don't get that behavioural change over time and stop that drink driving."
The scaling back started when National was in Government, but Mr Bishop said at the time now-police minister Stuart Nash "talked really big" of bringing the number up again.
"They've been in there [in Government] now for 18 months and the number of breath tests has actually fallen by 350,000 so I'd say it's really easy to talk big in opposition, it's a lot harder to deliver in Government," he said.
Mr Bishop said he was not confident, but hopeful the Government's new road safety strategy, to be announced by Julie Anne Genter in April, will increase the number of breath tests on New Zealand roads.