Many places of employment require their employees to submit to drug tests under certain circumstances. Unfortunately this practice is disproportionately discriminatory against cannabis users because the standard urine test for cannabis in New Zealand does not indicate current cannabis use, it only indicates use within the past 4-6 weeks. This is due to the test looking for the presence of the inactive metabolite as opposed to the active metabolite. Discriminating against a potential or current employee solely on the basis of their private cannabis use out of work hours is a breach of the New Zealand Bill of Rights. This page is a portal to information surrounding workplace drug testing.
In a rather worrying development, a new agency has been set up by ex-Police officers, to market large scale drug testing services to schools, parents and employers under the auspices of preventing intoxication at school/the workplace. What they don't tell their potential customers is that 70% of the positive results obtained by their tests are for cannabis, and that the test they use only indicates cannabis use in the past month. Therefore they are misleading their customers into thinking that they are preventing people from being intoxicated on the job/in school, but in fact they are unjustly punishing any person who has tried cannabis recently. This is a state of affairs that few employers, parents or schools would be comfortable with if they had been given full information. The evil organisation responsible for bringing wholly discredited US-style drug testing policies to New Zealand, without the approval of the public or the government, is the New Zealand Drug Detection Agency.
NORML New Zealand has a really good page outlining information about workplace (or anyplace) drug testing