The Council of Trade Unions says drug testing people on welfare is no more than beneficiary bashing after revelations Ministry of Health warned the Government its policy will cost twice as much as it saves.

President Helen Kelly said a memo obtained by the CTU shows the policy is a $14 million "waste of money". The Government could save up to $6m and was spending $1.9m on drug rehabilitation.

However, the ministry had warned more money would have to be spend on rehabilitation because recreational users could claim they were drug addicts to avoid losing 13 weeks of their benefits, she said.

"What the Ministry of Health is saying is that suddenly everyone will say they've got a problem because people can't afford to lose their benefits. They will fill up every rehabilitation programme in New Zealand."

Many people used marijuana occasionally and weren't impaired for work, Kelly said.

"These people don't have a drug addiction so it's a moral issue about crime rather than a workplace issue."

Marijuana was very much a working class drug, she said.

"Working class people are being penalised for what is a low level drug-taking because it has a legacy effect in your blood.

'Hard drugs don't show up because they go through your system very quickly.

"So they could be a recreational marijuana user who have used it once and two weeks later (fail a test). Where as you could be a heavy meth(amphetamine) user and not test (positive)."

The CTU didn't support people turning up for work under the influence of drugs but supported testing where employers believed workers were impaired, Kelly said.

"This sort of random drug testing is an absolute waste of money. This is a nonsense."

About 180 KiwiRail workers were about to lose their jobs, at a time when rail needed more Government investment, she said. The $14m could keep those 180 workers employed.

Social Development Minister Paula Bennett said today the difference between a recreational drug user and a drug addict was a difficult distinction.

"That is challenging and something we are going to have to work through," she told Radio New Zealand.

The ministry had been helpful in highlighting the challenges of the policy, Bennett said.

"We haven't implemented the policy yet. The policy and it's detail will be coming out in due course and then at that point the public can make their judgement on whether they think we've got it right.

"This is about us working through the detail. It's seldom that you have a policy that is nice, and doesn't have it's challenges and is simple."

There were potentially thousands of recreational users who were unable to work because of their drug taking, she said.

- © Fairfax NZ News