"Rather, it will leave many of them with exceptionally low or no income - a situation that undermines their likelihood for successful treatment."
The proposal is shaping up as a key election issue. Although the National Government has yet to announce its decisions on most of the Rebstock proposals, Social Development Minister Paula Bennett backs drug-testing.
"We expect it for people who're in work so why shouldn't we expect it for people who're looking for work? Frankly, I don't think that's too much to ask," she says.
But Labour is more sceptical.
"I can't see where a sanction [penalty] fixes the problem," says shadow welfare minister Annette King.
The local debate echoes arguments in other Anglo-Saxon nations, although in Britain ironically the party positions are reversed. Gordon Brown's former Labour Government gave job centres powers in 2009 to investigate beneficiaries with suspected drug problems and require them to undergo treatment or face benefit cuts.
David Cameron's new Tory Government repealed that law last year. Instead it is piloting contracts with treatment agencies for "payment by results", giving them financial incentives to get people back to work. This is also a key theme in Rebstock's broader welfare plan.
In the US, Florida has gone much further and has drug-tested all applicants for family benefits since July, refusing benefits for a year if they fail the test. Drug Foundation chief executive Ross Bell fears National could be heading in the same direction here.Employers drive reformDrug and alcohol addictions have not suddenly become a bigger problem than they have been for generations. What has changed is that employers have started taking the problem seriously. Air New Zealand set the legal precedent, successfully defending its drug testing policy against a six-union High Court challenge in 2004.
The forestry industry followed in 2008, requiring all forest owners and contractors to have "drug and alcohol-free workplace" policies backed by drug-testing.
Labour hire company Allied Workforce started drug testing at the same time.
"We started it, we take the credit for it, because we had a problem with the quality of people we were employing," says chief executive Mike Huddleston.
"Nearly every manufacturing company, every roading company, most construction firms, are now insisting on it."
Dr Paul Fitzmaurice of the Institute of Environmental Science and Research (ESR) says drug tests have increased from 30,000 to 40,000 a year three years ago to well over 100,000 a year. Paul Jarvie of the Employers and Manufacturers Association says testing now covers 40 to 50 per cent of the workforce.
Derek Baxter of the Certified Builders Association says employer attitudes to drugs have hardened.
"Perhaps a few years ago they were a bit more tolerant," he says. "Now they are not. It's tough enough employing people as it is, so they are less tolerant of potential problems."
The training sector is now testing too so that its trainees can work in the forests. Rotorua-based Waiariki Institute of Technology started drug-testing applicants for its 250-strong forest operations course this year and says Whangarei-based Northtec has done the same thing.
Balclutha-based Telford Rural Polytechnic said this week that it would drug-test all its farming students from next year.
Whakatane man Charlie James, who was addicted for 10 years to smoking cannabis and tobacco through a bowl of water, says failing a drug test when he applied for a job with Kawerau wood processor Kajavala Forestry gave him the strength to finally kick the habit.
"I was spending 70 per cent of my pay on it for 10 years," he says.
His partner of the past eight years never smoked, but until he was drug-tested he refused her pleas to stop.
"It was like, I don't need to give up, what for?" he said.
"I've had mates that have tried to give up for health reasons and couldn't do it. I've seen them, they can't, they are still going now.
"I was the same as them. It was just because of the job that helped me. If I didn't have an incentive it would be really hard."
His boss Jacob Kajavala says about a quarter of his 60 staff were regular drug users before he started testing them. Now productivity is up 12 to 15 per cent, staff turnover down from 10 per cent to 2.5 per cent a year - and workers such as James are happier.
"My health has got heaps better and I'm a bit more active," James says. "Sometimes I could be so wasted I couldn't even wash the dishes or vacuum the floor. Now I'll just get up and get into it straight away.
"And, I've been surfing all my life but now I'm surfing like two or three times a week, and even at work I feel more active. My breathing is better, my mind is better, clearer.
"My partner reckons this is the best I've been in the whole time we've been together."
Getting it rightDrug and alcohol problems are more common for beneficiaries than for workers. A 2007-08 Health Ministry survey found 55 per cent of young male beneficiaries aged 16 to 30 used illegal drugs (mainly cannabis) in the past year, compared with only 33 per cent of non-beneficiary males of the same age.
Across the whole working age group, 16 to 64, 32 per cent of (mainly female) beneficiaries, but only 18 per cent of non-beneficiaries, used illegal drugs in the past year.
A long-term study of people born in Christchurch in 1977 found that 12 per cent of those who were on welfare at any time between age 25 and 30 were abusing or dependent on cannabis by age 30 - but only 3 per cent of non-beneficiaries were.
But only 6345 people, or 1.9 per cent of the total 332,924 people on benefits last year, were on sickness or invalid benefits because of substance abuse. The vast majority of beneficiaries with addictions are on benefits for other reasons, such as sole parenthood, mental illness or simply not having the right education and skills to find work.
Conversely, the frustrations of unemployment may drive some people to drink or drugs after they end up on benefits.
The Drug Foundation warns that most of those who would fail drug tests, especially among young people, are only "recreational" dope smokers and not addicts at all. It says drug testing would actually make it harder for them to get work by labelling them with "a drug issue".
Robert Steenhuisen of Auckland's Community Alcohol and Drug Services, who co-chairs the National Committee on Addiction Treatment, says agencies would need extra funding to treat more beneficiaries on top of the 34,000 people they treat now, but they would be happy to work with Work and Income as they do now with the justice system.
"A substantial number of our clients are on benefits, but there is no formal relationship back to Welfare to report how it's going such as we have with the courts and Probation," he says.
"But it needs to be individualised and negotiated in consultation with the client and the treatment provider and the welfare agency. If you're going to have hard and fast rules that at the first sign of trouble you cut off the benefit, it's not going to work."
55 % of young male beneficiaries aged 16-30 (33 per cent of young male non-beneficiaries) used an illegal drug in the past year
32 % of all beneficiaries (18 per cent of all non-beneficiaries) used an illegal drug in the past year
12 % of beneficiaries aged 25-30 (3 per cent of non-beneficiaries aged 25-30) abuse or depend on cannabis by age 30.
2 % of beneficiaries are on benefits because of an alcohol or drug addiction.
* Understanding the issues around NZ's welfare reform and substance abuse policy www.drugfoundation.org.nz/policy/welfare-reform-and-substance-use