Alex White is stepping down as UnionsACT secretary to take up a role with the Australian Council of Trade Unions.

He will remain in Canberra for the next 10 weeks to help oversee the transition to a new secretary.

"It was a difficult decision," Mr White said.

"I've built up UnionsACT as a campaigning organisation that can have an impact on elections and on other issues. But one of the things that I've tried to do is make sure that if I was hit by a bus and I wasn't here, my team would be able to continue on.

"I'm very confident they can do that."

Mr White said his advocacy for workers' safety and campaigning on wage theft, marriage equality and sexual harassment in the workplace were among the highlights of his five-year stint in charge of the organisation.

A self-described "servant of the union movement", he has a fair share of friends and enemies in politics, the public service and the business community.

Unions remain a major driver of Labor Party policy, and policies championed by UnionsACT are often legislated by the ACT government.

The extent to which the organisation seeks to control Labor parliamentarians was called into question after Mr White ordered MLAs in 2017 to disclose any interactions with the Master Builders Association - UnionsACT's sworn enemy.

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The government's awarding of a $470,000 contract to UnionsACT to establish an advice service for young workers also raised some eyebrows.

Asked about the apparent closeness of UnionsACT and the Labor government, Mr White said: "We don't dictate anything".

"I think it's entirely unsurprising that a Labor government does things that are in the interests of workers," he said.

"Union members are members of the community and they have the right to have a government which cares about worker's issues. We have a government that actually gives a shit about workers and is willing to co-operate with them".

Mr White has at times been critical of and campaigned against the Barr government, including over controversial changes to compulsory third-party insurance.

But he has saved his most savage attacks for the building lobby and Liberal politicians.

UnionsACT launched a highly publicised bid to unseat Liberal senator Zed Seselja at last year's federal election, spending as much as $100,000 on its ultimately failed "Dump Zed" campaign.

Rejecting assertions the campaign was an outright failure, Mr White said there were swings away from Senator Seselja at polling booths which it targeted.

"The lesson from the election isn't that we shouldn't spend $100,000," he said.

"If we had more resources, it would have been a different story. We didn't spend enough money. If we spent three times as much, we would have got rid of him."

Mr White said UnionsACT had a far greater capacity to influence the local election, as the final spot in each of the five electorates could be decided by hundreds of votes.

Asked to forecast the outcome of October's election, he said Canberrans didn't want "climate-denying extremists" in charge. The claim came despite the Liberals last year reaffirming their support for the government's renewable energy and net-zero emissions targets.

Mr White also said that, like Liberal governments in other states, the Canberra Liberals would seek to privatise public assets - such as buses - if they swept to power. Opposition transport spokeswoman Candice Burch last week repeated that the Liberals had no plans to privatise Canberra's bus services.

Mr White also attacked the Liberals' economic agenda, claiming their proposal to freeze rates would "wreck the public service and increase unemployment". The opposition has maintained that freezing rates would only result in a 0.5 per cent hit to the government's budget.

The Canberra Times contacted the office of Opposition Leader Alistair Coe for a response to Mr White's claims.

In response, a Canberra Liberals spokeswoman said: "It's unsurprising that this union heavyweight would give an ideological spray on his way out the door. We're focused on cutting cost-of-living pressures on families and don't take much notice of these rants."

Community and Public Sector Union regional secretary and UnionsACT president Madeline Northam said Mr White had left the organisation in a great position to campaign for a "pro-worker" government at this year's election.

CFMEU assistant secretary Zach Smith said Mr White would be missed.

"Alex dedicated his time as secretary to protecting the rights of workers with an unflinching conviction, and has as a result bettered the working lives of Canberrans," he said.