The Government's plan to drug-test welfare recipients appears to be dead in the water, after Tasmanian Senator Jacqui Lambie confirmed she will not support the bill.

The plan, which would see 5000 new recipients of Newstart and Youth Allowance tested for illicit drugs, is due to be introduced to the Senate this coming Thursday.

Labor, the Greens and Centre Alliance have already said they won't support the measures, which meant Senator Lambie's vote was crucial in getting the bill across the line.

The Coalition and One Nation support the bill.

Under the plan, welfare recipients would be chosen at random for testing in three trial sites: Mandurah in Western Australia, Logan on the outskirts of Brisbane and Bankstown in south-west Sydney.

If they test positive for substances like marijuana, ice, cocaine, ecstasy or heroin once, they'll go on welfare quarantining. That means they would get their welfare money via a cashless debit card that would limit how they can spend it.

The welfare quarantining will last for two years after the initial positive drug test. If they test positive a second time, they will be referred to a healthcare professional who will discuss options like rehabilitation.

'They don't have my vote'

Senator Lambie told Hack on Friday that there aren't enough rehabilitation facilities in the trial sites for the bill to get her support. She pointed to the lack of support services in other parts of the country that are currently trialling the welfare card.

"As soon as the Government shows some good will and puts in the rehab and mental health services that are required and were promised in the trial areas of the welfare card, they can have my vote," Senator Lambie said.

That won't happen by Thursday or the end of this year and probably not next year. So... they do not have my vote.

The plan to drug-test welfare recipients was introduced prior to the last federal election, but failed to secure the support it needed to pass the Senate.

In 2017's MYEFO, or mini-budget, the Government set aside $10 million for rehabilitation facilities in the three trial sites, as a sweetener to get the Senate crossbench to support the drug-testing bill.

It didn't work, and the bill was shelved. It re-emerged after May's federal election, as the Government sought to try its chances with a new Senate.

Senator Lambie told Hack that the promise of increased services alone isn't enough. She's toured parts of the country that were promised support services when they signed up to trial the welfare card, but said they're still waiting for those services to be established.

Hack understands the Government will press ahead with plans to introduce the bill. The office of Social Services Minister Anne Rushton would not be drawn on what negotiations were underway with the Senate crossbench.