Leanne doesn't have a last name - or a return number - but she does have an earnest message about her father and the Turnbull government's changes to the age pension.

"I'm worried about my dad," Leanne says with pathos. "He's just had a letter from the government saying Malcolm Turnbull will be cutting his pension. He's a retiree on a fixed income and really needs the pension just to get by each week."

The robo-call is anonymous, with no authorisation or hint of its origin, but Fairfax Media has confirmed it is the work of the Australian Council of Trade Unions, which has launched an 11th-hour campaign against the January 1 changes.

The Abbott-era reforms, passed with the help of the Greens in 2015, will redistribute some income to needier pensioners while saving $2.4 billion over four years from the wealthy.

The asset limit will increase substantially, meaning those underneath it will gain an average of $30 a fortnight. But those above the threshold - about 330,000 people - will lose part or all of their pension.

Labor opposed the measure in 2015, but this year pledged not to wind it back. In recent weeks, pensioners have received letters from Centrelink informing them of the imminent changes.

Acting social services minister Mitch Fifield said the changes made the pension more sustainable and the family home would continue to be excluded from the assets test.

"Pensioners and their families should not believe the scare campaign from an organisation not even willing to put their name to their robo-calls," he said.

Fairfax Media has been told "Leanne", along with a pensioner used in a different recording, is not an actor but a real person whose father is affected.

"Him and mum worked hard their whole lives. So how can the government suddenly make changes now? And just before Christmas?" she asks in the robo-call.

"Have your parents got the letter too? The government can't get away with this. It's un-Australian. I'm going to call talkback radio and Malcolm Turnbull to tell him to get his hands off our parents' pension. If you could too, then maybe he'll listen."

Leanne then provides the phone number for Mr Turnbull's Sydney office.

The robo-calls follow Labor's controversial "Mediscare" campaign ahead of the July election, which involved calls and text messages asserting the government was planning to "privatise" Medicare. Some texts purported to be from "Medicare" itself.

Mr Turnbull was livid about the tactic, accusing Labor of frightening elderly people and undertaking "some of the most systematic, well-funded lies ever peddled in Australian politics".

The Liberal Party referred the matter to the Australian Federal Police, which ultimately dropped the investigation.

But Mr Turnbull has been unrelenting in his criticism, repeatedly raising the issue in Parliament and even in a six-minute tirade over Christmas drinks with the media at The Lodge.

He declined to comment on the ACTU robo-calls but was understood to be unhappy about the resurrection of tactics similar to the so-called "Mediscare" campaign.

ACTU secretary Dave Oliver said the cuts would upend the carefully-planned retirements of thousands of pensioners, and the ACTU would use "any means" necessary to fight back.

"Instead of addressing the substance of the policy and the damage their cuts are causing, the government continues to play the man and complain about the way we are bringing the issue to their attention," he said.

"We make no apologies about using any means to fight for those targeted by the cuts who have worked hard their whole lives and are entitled to a comfortable retirement."

Last week, a parliamentary inquiry into political communication following the 2016 election recommended laws be tightened to ensure messages such as texts and robo-calls contained appropriate authorisation.