The ABC’s flagship news programs including 7.30 and AM will be replaced by the BBC World Service when ABC journalists walk off the job for 24 hours for the first time in 20 years on Wednesday.

Staff are protesting what they say is a low pay offer from the ABC managing director, Hugh Marks, as well as work conditions and the broadcaster’s refusal to rule out replacing journalists with artificial intelligence.

ABC TV’s 7.30 with Sarah Ferguson will be cancelled on Wednesday evening while ABC News Breakfast will not air on Thursday morning as journalists, studio crew and directors go on strike.

Radio National Breakfast, AM, the World Today and PM will not air and music stations Triple J and ABC Classic will be play pre-programmed music without presenters.

The fate of the 7pm news bulletins remains unclear, as are plans to fill the ABC News channel.

Sources told Guardian Australia Radio National programming will be replaced by a BBC World Service simulcast, pre-recorded shows and repeats. Triple J will play music without presenters.

Radio current affairs program AM with Melissa Clarke will be broadcast on Wednesday before the strike, but not on Thursday as staff will not return until 11am. Late Night Live with David Marr will be off air on Wednesday.

Television’s ABC News Breakfast hosted by Bridget Brennan and James Glenday is not expected air on Thursday. The three-hour program needs studio crew and directors to function and, as members of the CPSU, they will likely be on strike.

The severe disruption to the public broadcaster’s news services will be triggered by protected industrial action by the journalists’ union, the Media, Entertainment and Arts Alliance (MEAA) and the non-journalists’ Community and Public Sector Union (CPSU), which represents staff in technology and control systems.

Over 1,200 ABC staff are MEAA members, according to the union, of about 4,500 total staff. About 75% of all staff voted on the offer, and staff were told they were 395 votes short of an acceptance.

Both unions have urged staff to reject the draft agreement of a 10% total pay rise over three years – 3.5% in the first year and 3.25% in the second and third years.

In January, Australia’s annual inflation rate was 3.8%.

Unions argued the offer was too low and failed to address concerns about the staff appraisal process, career progression, night shift penalty rates and reproductive health leave.

The MEAA encouraged presenters on broadcast television and radio programs to interrupt their work on Tuesday to deliver an on-air statement concerning the planned strike.

The directors of news and radio, Justin Stevens and Ben Latimer, emailed staff sharply reminding them to comply with the ABC code of conduct and editorial policies and “avoid making statements that could be interpreted as compromising impartiality on future matters you may be asked to report on”.

“Furthermore, any derogatory or disparaging comments about the ABC may amount to a breach of the Code of Conduct and may be addressed in accordance with disciplinary processes,” Latimer said.

The MEAA characterised the emails as “threatening”.

“You are legally protected to spend up to 5 minutes on air talking about why MEAA members are taking part in industrial action. It would be unlawful for the ABC to take any adverse action against you because you participated in that protected action,” the union said.

A number of radio presenters did tell the audience what was happening on Wednesday and apologised for the disruption.

Marks said he believed the revised offer “appropriately balanced” the needs of staff and audiences, and a higher offer would put ABC content and services in “peril”.

The ABC managing director has asked the Fair Work Commission for assistance to resolve the bargaining process after staff voted 60-40 not to accept the latest offer.

The MEAA said exemptions were in place to ensure emergency broadcasting continued, as ex-Tropical Cyclone Narelle continued its path around the north-west of the country.

Latimer told staff the radio networks would run a mix of syndicated and pre-recorded programming and local programming would vary across the states and territories.

The news division is expected to tell staff late on Tuesday what is planned for the schedule during the 24-hour strike, but their contingency plans have not yet been made public.