Work to recover the bodies has been halted because contractors have reached a 50m (164 ft) "exclusion zone".
Site owner RWE Npower said work cannot continue until the rest of the building is demolished.
Labour MP for Rotherham Sarah Champion said it was "one blow after another" for the men's families.
Four workers died when the plant collapsed on 23 February.
The company said it understood the news would be "deeply distressing" for their families.
The firm said it would use a demolition technique that would allow the standing remnants to fall away from the existing pile of debris.
Ms Champion, MP for Rotherham where two of the men lived, has been campaigning on behalf of the families.
She said the latest delay to the recovery work was a "national scandal" and warned there would be other such disasters in future and "the slow progress to recovering bodies can't happen again".
"For three months they have been trying to hang on to hope, now we just hope they will ever be found at all," she added.
RWE Npower added: "Our absolute priority is to recover their loved ones as quickly and as safely as possible.
"The remainder of the structure is currently considered unstable. Sadly, this means that, until the remaining standing structure can be safely brought down, we have restricted access to the recovery area."
The firm has announced plans to bring the rest of the building down by a controlled explosive demolition.
The bodies of Christopher Huxtable, 34, from Swansea, Ken Cresswell, 57, and John Shaw, 61, both from Rotherham, have not yet been found following the collapse of the boiler house.
Steve Hall, Mr Cresswell's son-in-law, has objected to the use of explosives at the site and said: "We want the men back in one piece, not many pieces."
The body of Michael Collings, 53, from Brotton, Teesside, has been recovered from the site.
The decommissioned Didcot A plant closed in 2013 and demolition work was taking place when it collapsed.
The cause is being investigated jointly by police and The Health and Safety Executive.
The failure to recover the bodies of three men killed when Didcot power station collapsed is a "national scandal", their families' MP has said.