A story about a driver smoking marijuana on his lunch break and then intending to continue his job recently caught a senior member of the Employers and Manufacturers Association by surprise.
Alan McDonald, who works as the head of advocacy and strategy at the Association, says he was told this anecdote by a Northland employer who believed marijuana use was as high as 90 per cent across his workforce.
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"I thought he was kidding, but he told me the guy was going to get back into his delivery truck and keep driving," McDonald says.
"That's the type of stuff we're up against now and if it's legalised it could become more of an issue."
Anecdotes like this aren't out of the ordinary, with McDonald saying that some employers don't even bother with testing because of the sheer quantity of staff that would be precluded from working.
The prospect of personal use marijuana being legalised has sparked widespread concern among employers, with McDonald saying that a recent survey of his association's members found that 73 per cent believed legalisation would have a negative impact on their businesses.
McDonald adds that while there is an emphasis on testing in the legislation, the two available methods – via saliva or urine – are also fraught with challenges for employers.
"If you use saliva tests, you'll get a positive for about two or three days. And if you use the urine test, you get a positive for about two or three weeks. There's no agreement on a standardised test."
McDonald worries this could have implications for employer liability if something goes wrong on-site or even in a company car.
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"Where does the liability start an end when it comes to these tests?" asks McDonald, pointing out that this could have insurance implications.
Depending on the test used, it could potentially lead to a staff member being deemed under the influence of cannabis as much as two to three weeks after using the substance. Could this give insurers an out, even when there is no real impairment of the worker?
"There is no real definition for impairment in cannabis," McDonald says.
"It's this grey area that we have a real concern with."
McDonald adds that while potency limitations might be a good step, they don't take into account how much a product a person might consume – particularly when it comes to the edible side of cannabis.
"The recommended dose might be to have five sweets and they instead eat 10 and then decide to go to work."
The counter-argument to all this is, of course, that many of these concerns have emerged during the black market and that regulation might help to address some of these problems.
However, McDonald points to research out of Colorado showing a significant increase in motor vehicle accidents among people who had consumed cannabis after the substance was legalised in the state. He also says that cannabis detected through workplace post-accident urine testing increased by 81 per cent in another study.
Other research has, however, shown that workers took 8 to 15 per cent fewer sick days in states where cannabis was legal, indicating that it may not have such a severe impact on the workforce.
The reality is, however, that employers will have to respond to the upcoming challenges that might emerge should recreational cannabis become legal.