The union SIPTU has said it will fight any compulsory redundancies for RTÉ staff.
It comes after RTÉ announced a plan to impose 200 job cuts at the national broadcaster.
Some of its star presenters will have to take pay cuts, while their studio in Limerick is to close, the RTÉ Guide will be put up for sale and their digital radio studios will shut down.
SIPTU's Karan O'Loughlin said: “SIPTU will oppose any attempt to enforce compulsory redundancies on staff in RTE. A plan for cutbacks at the national broadcaster, which was disgracefully leaked to the media yesterday, reveals plans to cut 200 jobs.
“The plan envisages that these job cuts will be achieved on a voluntary basis.
"It is unclear to our members how 200 voluntary redundancies can be achieved.
SIPTU, along with Equity Ireland and the Musicians Union of Ireland, represent around 1,200 RTÉ workers.
“These workers have been through several rounds of rationalisation at the station. They have taken the pain to assist in ensuring the survival of the crucial services which are provided by RTÉ and the thanks they have received is to be faced with an ultimatum concerning job cuts.”
RTÉ had intended to brief staff in full this week, but with the passing of Gay Byrne, a decision was taken to postpone the briefing until next week.
Ms O'Loughlin added: “What has made this situation even worse is the way this plan was exposed. Only senior management at RTÉ had access to this plan yet it was leaked to the media.
"This was extremely disrespectful to the loyal staff at the station.
“How this leak occurred is a matter that RTÉ Director General Dee Forbes must investigate and action must be taken against the culprit to deal with this extreme breach of trust.”
Meanwhile, Limerick's Mayor has called for a meeting with the Ministers for Communications and Culture to try and reverse RTÉ's plans close its Limerick regional studio and move Lyric FM.
Mayor Michael Sheahan said: “The news that RTÉ are closing their Limerick offices and moving production of Lyric FM to Dublin and Cork is very disappointing.
“Limerick has embraced Lyric FM and it has been seen as a badge of honour that the national station was based in Limerick. There was always a sense that Lyric was edgier and more innovative as it was located away from the shackles of Montrose.
"They have embedded themselves in Limerick life, more than their work in Lyric for example the Irish World Academy, The Irish Chamber Orchestra and our own Castleconnell Concerts.”
“I believe that the average cost per transmitted hour of programming on Lyric FM in 2018 was €800 significantly less than the cost for 2FM (€1,300), Raidió na Gaeltachta (€1,400) and Radio 1 (€4,000), so from a cost perspective it’s run extremely efficiently by a dedicated and multi-talented staff who also double as presenters/ producers.”
“I would urge RTÉ to look again at the decision to move Lyric FM and the impact it will have on the people whose jobs are now under threat. RTE must keep Lyric FM and the regional studio in Limerick in the interests of regional diversity and development.”