Hobart City Council's aldermen have voted to exempt themselves from its workplace drug-testing regime, which will be imposed on all other council staff.

At a meeting on Monday evening the exemption was voted to be upheld by aldermen, nine votes to three.

Under the council's draft Alcohol and Other Drugs Policy, council workers would be subject to random breath and saliva testing.

Some workers would be required to have no alcohol in their blood, some would be allowed 0.02 per cent blood-alcohol content and general workers would be allowed a reading of 0.05.

Unions representing up to 300 council workers were disappointed the policy would apply to everyone in the workplace, including ratepayers and visitors, except aldermen.

Kevin Midson from the Australian Workers Union (AWU) said he did not accept the argument council members were not employees.

"One day of the week, they're not a worker when it comes to testing for alcohol and drugs, two days later they suddenly are when it comes to superannuation payments," he said.

"So we're pretty disappointed that they wouldn't want to lead by example on a matter of safety."

Mr Midson said talks have been scheduled with the council.

"We will consider our options in terms of the Fair Work Commission and lobbying a dispute about the policy," he said.

"We'll continue to talk to the council like we always do but we just want the aldermen to get on board and to set an example."

Lord Mayor Sue Hickey said aldermen were not employed by the council in the same way as workers who would be subject to the random drug and alcohol tests.

"We have other rules and guidelines to live by," she said.

"We're also expected to go to an awful lot of public functions at which alcohol is served.

"Now, in many organisations you will find that there will be zero tolerance for anybody that drives equipment or machinery or deals with the public, and then you'll probably find that the CEO and the senior management must be below 0.05 reading, and in other organisations management have to self-certify that they're not drunk."

She said the unions were trying to use the issue as a bargaining tool in negotiations for a new pay and conditions deal.

"The Hobart City Council is not going to be held to ransom by the union arguing for a pay rise and that this is somehow rather a trade-off," Cr Hickey said.

The council is waiting for the State Government to release its model code of conduct for aldermen.

It will include a statement outlining the expectation that council members will behave responsibly with alcohol and drugs, and include a provision for self-testing.