The UK Government has confirmed it plans to sell off its helicopter maintenance facility near Perth.
Dara will be sold to Canadian company Vector Aerospace
Unions claim the proposal could lead to the eventual closure of the Defence Aviation Repair Agency (Dara) and have not ruled out strike action.
The MoD said the sale to Canadian-owned Vector Aerospace will guarantee the future of the site and the skills of the Perthshire workforce of about 300.
A facility at Fleetlands in Hampshire is also being sold.
Defence Minister Baroness Taylor said the business would probably shut in a few years if it was not sold.
Baroness Taylor visited Almondbank last month to see for herself the work done by staff.
In a written parliamentary statement she said: "In selling Dara we are confident that we are securing a long-term future for the business.
"My priority is ensuring our forces out on operations have the equipment they need to do their job and it is essential that we continue to maintain our aircraft to the highest standard.
"I pay tribute to the dedicated and highly skilled employees at Almondbank, doing a fantastic job to support our troops in Afghanistan, Iraq and at home by ensuring our helicopters are fit to fly.
"If we do not sell, there is no doubt that the business at Almondbank could decline rapidly and probably close within a few years, leading to serious job losses.
"We want to retain such a highly skilled and valuable workforce in Scotland. But with decreasing workload due to a number of our aircraft starting to go out of service, diversification into the commercial sector is the best solution."
Vector Aerospace chairman and CEO Don Jackson said: "There is a significant amount of synergy between the Dara businesses and Vector's current global operations.
About 350 staff help repair Ministry of Defence helicopters
"We are looking forward to growing the level of support that we are providing to the UK MoD and to working with the employees at Almondbank and Fleetlands [the Dara site in Hampshire] to create a centre of excellence in European helicopter maintenance.
"We have expansion plans and hope to increase our staff numbers as appropriate."
National officer at the Unite union, Ian Waddell, said: "Our members are bitterly disappointed that the government have taken the decision to turn their backs on years of loyalty and hard work.
"At this point the union will not rule out strike action.
"The workforce at Dara are a critical asset and vital to the nation's defence.
"We firmly believe that this work belongs within the public sector."