UP to seven out of 10 of Scotland's police control rooms are facing the axe with the potential loss of hundreds of civilian jobs.
Staff union Unison said it "feared the worst" as Chief Constable Steven House prepared to reveal the most radical reshaping of 999 call services in decades.
Senior officers at Police Scotland, including Mr House, have long hinted that they are looking to shut most of the existing control rooms - which also handle calls to the non-emergency 101 number -and focus on three, four or possibly five regional centres.
Insiders expect the announcement to hit the West of Scotland, which has three of the existing 10 units, including one at the old Strathclyde force HQ in Glasgow's Pitt Street, which is itself earmarked for closure.
There is also a more modern facility in Govan and another in Motherwell.
The move - details of which will be revealed later today - is designed to help Mr House find more than £1 billion in savings from the new single force over the next 12 years.
However, unions and opposition leaders believe the cuts, on the back of a review of police stations and counters, mark a retreat from local policing and threaten the jobs of front-line professionals.
Gerry Crawley, of Unison, said: "We have deep concerns about the potential job losses - and the loss of local policing services, which follows the review of police stations.
"Unison hopes the announcement due today is not going to result in the decimation of support staff jobs but we fear the worst. We are talking about hundreds of jobs."
Scotland's 10 control rooms currently employ around 1000 people.
Mr House has been open about his intention to close control rooms. Last year he said he thought four such units would be enough.
He added: "I'd be very surprised if there remained 10 control rooms, it's not a sustainable model.
"You might have needed it for eight police forces, but for a single police service for Scotland you would probably need three or four control rooms."
Police sources have always said they believe the rationalisation of control rooms - and the loss of their civilian jobs - was an inevitable consequence of the new single force, backed by the SNP, Labour and the Tories.
Nationalist ministers routinely stress that they are protecting what they insist are front-line services, including a pledge on police officer numbers, rather than backroom operations.
Only the Liberal Democrats opposed the creation of the single force. The party's justice spokeswoman Alison McInnes last night linked control room closures to what she described as the SNP's "obsession with power-grabbing centralisation".
Some control room staff have already signalled that they want out as they prepare for the axe. Last year it emerged that control room staff made up around 300 of the 2000 civilians who applied for voluntary redundancy or early retirement from the new force.
Senior officers, however, asked for such applications to be put on hold pending today's announcement.
Workers, unions and other stakeholders will today be briefed on the details of the proposals, which will then go before a meeting of the force's watchdog, the Scottish Police Authority, next week for approval.