Public servants at Centrelink, Medicare and Child Support will begin strike action on Friday afternoon aiming to force a breakthrough in a bitter industrial dispute.
The Community and Public Sector Union said employees would hold rolling strikes for seven hours from 1.30pm, and that limited work bans had started.
Workers will strike after recent talks aimed at resolving their enterprise bargaining dispute with the Department of Human Services failed to break the impasse on pay and conditions.
The department warned the industrial action could reduce staff numbers in service centres and on phones, and directed clients planning to use Centrelink, Medicare or Child Support services to online and self-service options.
It said the strike would not affect ongoing customer payments.
The DHS vowed it would remain unmoved by strikes and said it was "disappointed" the CPSU would take industrial action while negotiations continued.
It would provide staff with a vote on a new enterprise agreement "as soon as possible".
"The industrial action will not change the department's position in terms of negotiations for a new enterprise agreement."
CPSU national secretary Nadine Flood said the dispute had lasted too long.
"It's bad for people working in Medicare, Centrelink and Child Support, it's bad for their families and it's bad for the essential services our members in DHS provide," she said.
Strikes will start after industrial action planned by Centrelink public servants around Australia in February was cancelled when their employer and union agreed to more talks.
The agreement was reached as the two sides met at the Fair Work Commission in Canberra to hear an attempt by the DHS to have the strikes by workers at Centrelink, Medicare and the Child Support agency ruled illegal.
The CPSU has threatened more strikes and says while it has made progress with other agencies still without new agreements, its stand-off with the DHS shows no signs of ending.