Centrelink public servants have stepped up their internal resistance to the welfare agency's controversial "robo-debt" program, with union officials handing out protest material to clients at offices around Australia on Wednesday.

The move came as the welfare agency lashed out, again, at "unsubstantiated claims from anonymous staff" about the debt recovery program.

Centrelink has been embroiled in controversy since late 2016 over its debt collection system. Credit:Getty Images

Centrelink offices in all states and territories were being targeted by the staff-written pamphlets, which are being handed out by members of the Community and Public Sector Union, on Wednesday. Visitors were told Australia's welfare agency is in crisis and that it is getting worse.

In New South Wales, Centrelink shopfronts at Liverpool and Penrith were being targeted for the action.