The trade union Unison said it "feared the worst" for the future of its members as chief constable Sir Stephen House prepared to announce the most radical reshape of 999 call services in decades.
It comes amid warnings that the move will threaten local policing and particularly affect residents of rural areas who report crimes.
Sir Stephen and other senior officers at the single force are understood to be looking to shut most of the existing control rooms, which also handle calls to the non-emergency 101 number. The plan is to retain between three and five regional hubs.
Fire and ambulance control rooms have already undergone similar "rationalisation" programmes, sparking claims of centralisation from opposition politicians.
Police Scotland's cut-backs are expected to save more than £1 billion over 12 years.
Gerry Crawley, Unison's Scotland Regional Organiser, said: "We have deep concerns about the potential job losses across Scotland - 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 across Scotland, but we fear the worst. We are talking about hundreds of jobs."
The union is particularly worried over the impact the review will have on services outside the major cities.
Mr Crawley added: "There will likely be a disproportionate impact on rural parts of Scotland."
Scotland's 10 control rooms currently employ around 1000 people, with three in the former Strathclyde force area. They include the one at the old force headquarters at Pitt Street, Glasgow.
The building is already scheduled for closure, with insiders suggesting its control room's future is in immediate doubt. There is also a more modern facility in Govan and another in Motherwell, North Lanarkshire.
Control rooms also exist in seven other former police force areas, at Bilston Glen near Edinburgh and in Inverness, Aberdeen, Dumfries, Glenrothes, Stirling and Dundee.
Shortly before the single force started work last April, Sir Stephen said that 10 control rooms were unlikely to be needed for a single force.
Liberal Democrat justice spokeswoman Alison McInnes said control-room closures were linked to the SNP's "obsession with power-grabbing centralisation".
She added: "Until now, frontline police control rooms have ensured that the vital local knowledge needed for time-critical emergencies has been valued and nurtured.
"The SNP Government's lack of respect for local communities has allowed the axe to fall on our courts, police counters and now police and fire emergency control rooms."
Around 300 of the 2000 civilians who applied for voluntary redundancy or early retirement from the new force are waiting for today's announcement.
A Police Scotland spokesman said the force is reviewing all areas of business, adding that this included "the current structure of our Contact Centres and Control Rooms. Any changes will be subject to full consultation with staff and approval of the Scottish Police Authority."
An SNP spokesman said: "While the Scottish Government is protecting police at the front line with 1000 more officers on the beat than in 2007, the LibDems in partnership with the Tories are responsible for cutting over 15,000 officers south of the border.
"The SNP has a record of delivering when it comes to policing and security and we will take no lessons from a party that has presided over massive cuts to officer numbers elsewhere in the UK."