A 24-hour strike began at 11am AEDT on Wednesday as staff protested against the widespread use of short-term contracts and limited career progression, along with a pay deal offering a below-inflation increase.
ABC's main news channel will lean heavily on BBC World News throughout Wednesday while a re-run of Australian Story will replace the 7pm news bulletin on the broadcaster's main channel.
A Hard Quiz re-run will replace flagship current-affairs program 7.30.
Some radio programming will be replaced by BBC content.
Journalists, camera operators, technicians and other staff rallied outside more than 60 ABC offices, including in Melbourne and Sydney, as the strike began.
Hundreds of workers walked out of the Ultimo office in central Sydney shortly after 11am, waving flags and holding signs including some that read "fair pay, it's as easy as ABC".
"Quality jobs represent quality news and content," ABC journalist and media union division president Michael Slezak told the crowd.
"We won't let the ABC be run into the ground by ideological corporate managers who refuse to listen to staff."
On-air presenters, including those set to strike, used their platform on Wednesday morning to inform viewers about the industrial action.
ABC Radio Melbourne Mornings host Raf Epstein addressed the strike on air, explaining it as an argument over how best to provide sustainable, secure work.
"Staff and management really do agree on you being the priority and providing you with some quality programming," he told listeners.
"Staff and management disagree on how we get those sustainable and secure jobs."
The airwaves were then filled with 1988 hit Waiting for a Star to Fall.
In a shot showing mostly empty desks, ABC24 host Gemma Veness reminded viewers about the strike and its impact at about 10.58am.
"The ABC is planning to continue delivering some services and emergency broadcasting will not be affected by the strike," she said.
ABC managing director Hugh Marks said he had broadened the definition of emergency broadcasting from only applying to fires, floods or other natural events.
"It's important, if there is a matter of national or international importance that happens while you know the staff are on strike, that we're able to call staff in," he told ABC Sydney.
When asked if management could invoke it for the growing fuel crisis, Mr Marks said it "depends on how those matters progress".
He defended the last rejected pay deal - 10 per cent across three years - as financially responsible and competitive for the industry.
The average tenure at the broadcaster was more than 10 years, he said.
Liberal Senator Sarah Henderson, a former ABC journalist turned critic, told her former colleagues to accept the "pretty good deal" while attacking presenters for "hijacking" news programs to explain the strike to listeners.
"I say shame on ABC staff who've made this decision. Australians deserve much better than this," she said from outside ABC offices in Parliament House.
The Community and Public Sector Union and the Media, Entertainment and Arts Alliance say they want an offer that reflects cost-of-living pressures, boosts career progression, and provides certainty for hundreds of staff on rolling short-term contracts.
"ABC plays such an important role in our society and in Australian storytelling and it's really important ABC management come to the table," CPSU national secretary Melissa Donnelly told AAP.
The unions are also demanding greater night-shift penalty rates, reproductive health leave and rules relating to artificial intelligence.
It is the broadcaster's first major strike since 2006, with a smaller strike in 2023 including only staff who were CPSU members.
More than 4400 people work at the ABC, including 2000 in news, the largest division.
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