GE has confirmed it plans to transfer substantial work from its aero engines plant in Prestwick, Ayrshire, to Taiwan because a plant in the Far East has a "more attractive cost profile".
It has given details of the jobs risk to staff at its Scottish subsidiary, GE Caledonian.
The Unite union, which recently won a recognition battle at the plant, believes the workforce will drop to 450 after the latest redundancies. Early last year the total number of staff was 805.
The company, also widely known as General Electric, says it will keep 500 staff at Prestwick.
Unite regional officer Paul Neilson said: "This is a planned and deliberate removal of specialised work to a low-cost site in Taiwan, which is likely to result in significant compulsory redundancies, reducing the workforce to almost half the number at the start of 2013.
"It is apparent Unite and its members are being blamed for this loss of work, rather than General Electric acknowledging the real issue: an ongoing failure by management over many years to fully utilise a highly motivated, multi-skilled and professional workforce to remain competitive."
Company sources denied the decision to move work to Taiwan was in any way linked to the recognition of Unite at Prestwick after a decade-long battle.
GE Caledonian has a decades-long track record of reconditioning or overhauling aero engines at Prestwick, part of a wider Scottish industry making and repairing high-tech aviation components that includes plans operated by arch-rival Rolls-Royce at Inchinnan, Renfrewshire, and East Kilbride, Lanarkshire.
The aero engines business has boomed in recent years, with aviation quick to recover from the international economic downturn of 2008. However, companies have been eager to relocate some of their work to low-cost centres. The Herald understands the costs per hour of work in Taiwan can be less than half of those in Scotland.
GE Aviation, the US conglomerate's Ohio-based engines company and owner of GE Caledonian, announced a proposal to "transition" work on its CF6-80E engines from Prestwick to a firm called Evergreen Aviation Technologies in Taiwan. It is this plan that, if implemented, will cost up to 173 jobs.
It said Prestwick would now focus on its work overhauling other engines, the nearly identically named CF6-80C, and develop capacity to do the same for the GEnx, the next generation dual rotor jets designed for aircraft such as Boeing 787 Dreamliner.
Patti Leary-Kreitzer, site leader at GE Caledonian, said: "There is more competition in the overhaul sector than has ever existed before, especially for our legacy engine models.
"This, combined with the impact of the economic recession, has seen customers wanting high quality, low cost options for engine overhaul.
"We are responding to this by continuing to drive productivity at existing plants so as to lower costs, as well as seeking new opportunities to provide low cost alternatives.
"Before any final decision is taken regarding the implementation of this proposal, the company is fully committed to engaging in formal consultation on the matter for a minimum period of 45 days."
Mr Neilson said: "Unite will be entering into consultations with GE shortly and will work for a review of this decision to minimise the impact on our members, their families and wider communities."