Delphi Diesel Systems has confirmed it will gradually wind down manufacturing operations at its Sudbury site as a "result of predicted falls in the demand for diesel vehicles".
The US-owned company makes diesel fuel injectors and filters for commercial vehicles at the plant.
The Unite union said it understood the owners plan to move work to Romania.
In 2015, the company cut 176 jobs in Sudbury and moved the work to eastern Europe.
A statement from the firm said: "Delphi is sensitive to the implications of this gradual wind down and will work closely with worker representatives to minimise the social impact from this decision.
"A programme will be put in place to help employees find alternative employment in the region or to relocate to other Delphi facilities."
Unite said the Sudbury plant makes a "healthy six-figure profit each month" but that the work is going to move to a country where labour costs are generally cheaper.
The union's assistant general secretary for manufacturing, Tony Burke, said: "The news reinforces the need for a strong and robust industrial strategy to be activated immediately to secure these highly-skilled manufacturing jobs so they remain in the UK rather than move to a low-cost country.
"It is time for the Business Secretary Greg Clark to translate the rhetoric of an industrial strategy into practical action to secure essential UK manufacturing jobs, especially in rural Suffolk where such skilled industrial jobs are thin on the ground."
A government spokesman said: "This is clearly a worrying time for workers at Delphi in Sudbury and their families. Jobcentre Plus will stand ready to help people get back into work as quickly as possible.
"The government's industrial strategy aims to build on our strengths as a country while addressing the long-term challenges we face.
"Later this year we will deliver an industrial strategy white paper that will help to build an economy that works for all."
An engineering firm is to close a plant in Suffolk with the loss of 520 jobs by mid-2020.