An internal investigation has revealed Victoria Police officers faked more than 250,000 roadside breath tests over a five-year period.
A statement from Victoria Police said some officers had been placing a finger over the breath tester's straw entry hole, or blowing into the straw themselves, in an attempt to distort test results.
The Professional Standards Command and statistical specialists found 1.5% of all tests had been falsified after looking at more than five years of police breath test activity.
"This conduct will not be tolerated," said Professional Standards Command assistant commissioner Russell Barrett. "Any member found engaging in this practice from today has been put on notice they will be investigated.
“I had not heard of our members engaging in such a practice, we let ourselves down, we’ve let the community down. It stops now.”
Following the internal review, Victoria Police will appoint an external investigator to provide advice on the cause of the behaviour, and aggravating circumstances that could be referred for further investigation.
Barrett said he believed the tests were faked in an effort to "hide or highlight" productivity, and that regular audits were now being considered.
"Whatever reason our workforce may come up with, it isn't acceptable."