Centrelink staff are worried they will face still more violence and aggression from desperate beneficiaries.

And one of the sites where drug testing is planned - Logan, in Queensland - has told the government it doesn't want to be involved. The Logan City Council said the trial, in which 5000 people applying for Newstart and Youth Allowance at three sites across the country will have to pass drug tests to get their benefits, will lead to more crime, mental health problems, financial hardship, stigma and marginalisation.

In a submission to a Senate inquiry into the drug-testing bill, the council said if the government pushed ahead despite opposition, it should use saliva testing, which would detect immediate drug influence, rather than hair or urine testing.

The government is trying for the third time to get its drug testing regime though the Senate. It says Centrelink would choose people at random when they apply for Newstart and Youth Allowance. They would be called in for an appointment, where they would be told they had to take a drug test - which would be done either on Centrelink premises or in the offices of the contracted drug-tester.

The government says it will write up protocols on how tests should be done once the legislation has passed. The protocols released in 2017 said tests should be done by someone of the same sex as the person being tested if practicable, and it shouldn't involve the removal of more clothing or more visual inspection than was necessary for the test.

If someone doesn't turn up for their appointment or refuses a test, the payment is cancelled. If they fail a test, they are put on two years' income management, where most of their benefit is attached to "Basics Card" and can only be spent at some shops, with alcohol, cigarettes, gambling and pornography all banned.

If someone fails a test, they will also be tested a month later and if they fail again they will be referred to a medical professional, who can recommended treatment including counselling or intensive rehabilitation or drugs such as methadone, which will be compulsory.

If someone want a second test to check the results, they must pay for it themselves - with the cost of the second test docked from their Newstart payments.

But groups representing psychiatrists, doctors, specialists, drug treatment and other organisations are trenchantly opposed.

They point to drug tests being unreliable, with people on prescription antidepressants and other medications liable to test positive to amphetamines, and people taking cannabis testing positive for days or weeks after smoking.

The Royal Australasian College of Physicians said given the risk of false positives, medical practitioners with the right expertise would be needed to assess results. Only medical practitioners should have access to people's health records, and make decisions about treatment.

"What qualifications, training and experience in drug and alcohol medicine would a Services Australia contracted medical professional who undertake assessments be required to have?" the group asked.

The testing regime could also encourage people to turn to other more dangerous drugs are that are not tested for, such as synthetic cannabis or fentanyl.

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The Community and Public Sector Union said the plan would not work and was likely to mean more aggression against Centrelink staff.

Staff were already hugely concerned about dealing with people on ice, and had less security and support in regional areas, the union's Melissa Donnelly said in a submission.

"[Department of Human Services] staff are seen as the face of government, and are often held responsible for implementing government policy. This means when a policy is seen by a DHS client as adversely impacting their life, this can lead to an increase in customer violence and aggression towards DHS staff. While the overwhelming majority of DHS clients do not respond violently to decisions of this nature, many of them do become angry and desperate."

The Australian Medical Association, which represents doctors, said random drug testing did not distinguish between people who were one-off or occasional drug users and addicts.

It said urine and hair tests were far more invasive than saliva, with urine testing stressful for some people. Hair testing should not be dropped, because it showed the presence of drugs for months after they are consumed.

And it called on the government to be specific about the drugs it would test for, with the bill listing methamphetamine, cannabis, ecstasy, heroin and cocaine, but also allowing testing for other drugs that are not listed.

Royal Australian and New Zealand College of Psychiatrists said the plan was ill-founded, lacked evidence and could cause more harm to people already vulnerable, increasing poverty, crime and homelessness. There was no evidence that mandatory testing reduced drug use.

The money - estimated at $500 to $900 a test - should be spent on addiction services, which were already stretched.

Unemployment itself was associated with poorer mental health and requiring drug testing could mean humiliation and belittlement of the recipient and exacerbate the stigma. It could make it even more difficult for people to manage everyday demands, president John Allan said.

The Public Health Association said the drug-testing proposal had already been rejected by the Senate, in 2017 and 2018, and the new bill was substantially the same other than adding cocaine and heroin t the drug list.

The proposal was "punitive, coercive, ill-informed and destined for failure", chief executive Terry Slevin and president David Templeman told the committee in its submission.