Pick up the phone tonight and you might find a stranger on the line: Leanne.

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.