Unions fear up to 200 jobs will be axed under plans by the BBC to make fresh savings of £150 million to address a funding shortfall.
The corporation will be pressed to give guarantees of no compulsory redundancies in the latest round of cuts.
The corporation has previously announced plans to cut 1,000 posts, with around 300 already gone or being consulted on.
Officials said it was too early to say how many further jobs will be lost as part of the additional savings measures announced today.
Of the £150 million, around £50 million will be saved by creating a "simpler, leaner" BBC, with fewer divisions and senior managers and fewer layers between the top and bottom of the organisation.
Another £35 million will be saved from BBC TV's sports rights budget, leading to the loss of some existing rights and events.
A further £12 million in savings will come from the BBC's TV budget.
Drama will be protected, but there will be reductions to factual, comedy and entertainment, although savings from The Voice will be used to develop new, home-grown formats.
The BBC also announced that £12 million will be cut from BBC Online, and £5 million from news, including efficiency savings from a review of working practices, terms and conditions, and commercial income or cost reductions in BBC Monitoring, subject to approval from the BBC Trust.
Director-general Tony Hall said: "The BBC has and is doing everything possible to make sure the impact on the public is minimised. Wherever possible we're targeting savings by creating a simpler, leaner BBC.
"But cuts to budgets for programmes and services are unavoidable. No director-general wants to announce reduced spending on services that the public love. This is very tough, but the BBC's financial position means there is no alternative."
The £150 million set out today is part of the £700 million overall savings the BBC must find due to the flat licence fee agreed in the summer.
An announcement of how the remaining £550 million savings will be met by 2021/22 will be made in the spring, but the BBC said these are likely to include major structural changes to how it works and fulfils its mission to inform, educate and entertain.
Gerry Morrissey, general secretary of the Bectu union, said: "We will oppose any compulsory redundancies."
Michael Dugher, shadow culture secretary, said: "Under this Government, we are seeing the sad decline of the BBC.
"People will be disappointed that there will be less sport on the BBC and that they could lose the BBC's popular Red Button service.
"This looks like just round one of cuts, given that the Government has now lumped the BBC with the cost of funding free TV licences for the over-75s. Ministers need to get their act together and deliver on its promise to close the iPlayer loophole that is costing the BBC dearly.
"Under this Government, the BBC is at real risk. Ministers want to cut down the size of the BBC even further and narrow its remit as part of the Charter Renewal process."