Private firms which manage thousands of offenders in Wales and south west England have gone into administration.
Working Links community rehabilitation companies will hand over their work to a firm running the service in south east England.
The Ministry of Justice (MoJ) said it had "taken action to ensure continuity of probation services".
The union representing probation officers has now called for an urgent meeting with the minister responsible.
Ian Lawrence, general secretary of Napo, said: "This is exactly what we warned the government about from day one of this disastrous privatisation programme that has seen an award-winning service fall into total chaos in just four years."
The management of low-to-medium risk offenders was privatised four years ago.
Working Links was given the contract for Wales, as well as Avon and Somerset and Devon and Cornwall.
Last year a further shake up of the service was announced following a number of damning reports and recognition that the funding model for the CRCs wasn't working.
A Ministry of Justice spokesman said: "We were aware of Working Links' financial situation and have taken action to ensure continuity of probation services.
"That means probation officers will continue to be supported, offenders will be supervised, and the public will be protected.
"The chief inspector's report on these CRCs lays bare their unacceptably poor performance and we will work closely with the new provider to urgently raise standards."
Dame Glenys Stacey, chief inspector of probation, welcomed the MoJ's move and said it "should be a turning point".
"Ministers recently took the decision to terminate all 21 CRC contracts early, next year," she said.
"The secretary of state is now considering what comes next. Our CRC inspection evidence shows a variable picture but it is one in which the provision of services in most cases is wanting, often significantly so."
In Wales, the service is also due to be renationalised next year and the MoJ said it will be looking at bringing this forward.
But there is anger from the union, which says the government should have stepped in before the firm went into administration.
"Napo has continually pleaded with ministers to terminate the contracts between the MoJ and Working Links following highly critical reports from HM Inspectorate of Probation and a litany of high profile Serious Further Offences including a number of murders," said Mr Lawrence.
Among those murders was that of Conner Marshall. The 18-year-old was killed in Porthcawl in 2015 by David Braddon who was being supervised by the CRC, but had missed eight probation appointments.
- The Cardiff-based Wales CRC employs about 430 staff in 23 offices across Wales
- It manages nearly 9,000 offenders, according to the most recent figures
- Unions say nearly half of jobs have been cut since the contract was awarded
- The CRC also posted a loss of £2.1m in its last published accounts after a period of "heavy change and restructure".
Napo last year gave evidence to the Commons' Welsh Affairs Committee inquiry into prisons, expressing concern about staff shortages and unpaid bills - including bailiffs raiding the Cardiff office to seize equipment.
It also said there was a human cost, giving the example of an offender having to cancel their only contact days with their child for three weeks in a row to attend community work - only to see each session cancelled because of staff shortages.
Meanwhile, the Bristol, Gloucestershire, Somerset and Wiltshire CRC - which has about 256 staff - has also made losses over the last two years, including £1.8m in 2017. It deals with about 6,300 offenders.
The Dorset, Devon and Cornwall CRC, which employs 173 staff and deals with about 4,100 offenders, had made a £1.5m loss.
Both saw staff numbers cut by a third in the year to 2017.
The probation inspectorate published a report into Dorset, Devon and Cornwall CRC on Friday which it called "thoroughly dispiriting," with staff "trapped in a spiral of decline".
Inspectors found staff were under-recording the number of riskier cases because of commercial pressures. They were also completing offenders' sentence plans to meet performance targets, without actually meeting them.
Working Links was bought out by German company, Aurelius, in 2016 and the three contracts are now being handed over to Seetec, which currently runs the service in Kent, Surrey and Sussex.
Seetec executive director Suki Binning said the immediate priority was to stabilise the service after what had been a "challenging and uncertain period" for probation teams.
"While we recognise that confidence in probation services is shaken and do not underestimate the challenge and complexities ahead, we are determined to build a viable and sustainable service that maintains the confidence of communities in the south west and Wales," she said.
Unison's officer for police and justice Ben Priestley called for the collapsed contracts to be brought back in-house
"This privatisation has been a disaster and one we had long predicted," he added.