Immigration services based in Britain, Canada and Sydney will move to a Datacom hub in Adelaide in a decision Home Affairs Minister Peter Dutton says will reduce wait times, but the Community and Public Sector Union says the three-year contract will devastate workers and give the government less value for more money.

Home Affairs said the decision would not cause 250 job losses, and that it was working to redeploy staff.

"A number of job opportunities have already been identified and many staff have already made the transition to other areas within the department or have been notified of their permanent placements," it said.

Home Affairs, which first flagged the move in its previous form as the Immigration department, said the contract would reduce its share of high volume, labour-intensive but relatively straightforward work, letting the new mega-department focus on complex and high-risk matters.

CPSU acting deputy secretary Brooke Muscat-Bentley said the change would hit people relying on the department to navigate Australia's complex immigration rules.

"Staff in the current call centre are well-trained and work under strict Commonwealth guidelines to ensure the sensitive personal information they have access to is protected," she said.

"By contrast we have serious concerns about the training and protections that will be in place under Datacom."

Home Affairs said staff accessing its systems had to undergo screening and receive a security clearance.

It would regularly review Datacom's security controls for compliance with security and privacy legislation and standards.

Ms Muscat-Bentley blasted Home Affairs' choice of contractor, saying Datacom had a poor track record on staff wages and working conditions.

Despite profits from Commonwealth contracts, it may be artificially reducing its profits to reduce tax liabilities, she said.

Datacom referred Fairfax Media to a statement saying it fully complied with financial and legal obligations.

"With regards to Australian tax obligations, Datacom pays the full corporate tax rate of 30 per cent with deductions for the R & D offset," it said.

Datacom will take over the call centre work, which involves 1.5 million incoming calls each year, from Home Affairs' Sydney Service Centre where departmental employees answered questions about visas, citizenship and responded to other compliance queries.

Two overseas centres, provided to cover different time zones, will also lose work to the private sector.

The offices took calls from a wide base of users, including businesses with inquiries about sponsoring overseas workers, and have traditionally been an entry point for public servants to get a start working with the department.

Do you know more? Send confidential tips to ps@canberratimes.com.au

Home Affairs boss Michael Pezzullo told his public servants in his post-budget address last year that the call centres were to go private.

Datacom will begin the call centre work in full by mid-2018.

Government use of contractors has come under increasing scrutiny, while an unprecedented move by Centrelink drew fire when Serco won a 250-job contract last year to take calls about payments in a three-year pilot program costing $51.7 million.

Follow Doug Dingwall on Twitter.