Staff at an engineering firm in Sudbury have been told the plant is to close with the loss of more than 500 jobs.

Delphi Diesel Systems, whose factory is based in Newton Road, has announced the site will be scaled down before finally closing in 2020, despite being “highly profitable”.

In June, the company, which makes diesel fuel injectors and filters for commercial vehicles, announced it was entering into a consultation about the long-term future of the plant.

The union Unite says it understands that the American-owned firm plans to move work to Romania for cheaper labour costs and greater government subsidies.

Unite called on the government to step up its industrial strategy following the announcement and it is understood that 50 jobs will go between now and Christmas.

Tony Burke, Unite assistant general secretary for manufacturing, said: “The news from Suffolk today 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. The minister needs to accelerate into top gear.”

Neal Evans, Unite regional officer, said: “We definitely believe that the company jumped the gun, putting the jobs of the workers and the security of their families in danger, as it did not allow enough time for alternatives to be developed.

“What is happening here is that the work at the Sudbury plant, which is making a healthy six-figure profit each month, is being sent to Romania where labour costs are lower and subsidies are greater.

“The company has said that some of the work would be transferred to another site in Gloucestershire, but we have no written assurances that this will be the case.

“We will continue to campaign for the company to reverse the closure and we desperately need a pro-active and coherent industrial strategy as the country faces up to the daunting economic challenges of the post-Brexit world.

“We are also disappointed that not one of the East Anglian Tory MPs signed the House of Commons Early Day Motion (EDM) motion expressing ‘grave concern’ that more than 500 jobs at the profitable in Suffolk site were under threat.”

The news comes after the government announced new diesel and petrol cars and vans will be banned in the UK from 2040 in a bid to tackle air pollution.

• In June, MP James Cartlidge warned Sudbury must remain commercially competitive if Delphi closed

South Suffolk MP James Cartlidge said: “Clearly this is bad news and will be a blow to all employees at the plant.

“It is well known that the plant has been successful and profitable, and that the workforce is of the highest quality.

“However, we already knew that the plant faced a challenging future, and that when the consultation was announced most people appreciated that there was a relatively high probability of the plant being closed because of the structural market shift away from diesel.

“Indeed, just in the last week we have had further confirmation of the reality of the challenge facing diesel producers with the government announcing a ban on the sale of new diesel cars and vans from 2040.

“Obviously, the closure of the plant is not a direct result of the government’s announcement, but it underlines the reality that the whole automotive industry is moving away from diesel propulsion and towards a new future of more environmentally-friendly engine systems.

“I understand there will be around 50 redundancies between now and Christmas, and whilst this is bad news, it is nevertheless a positive of sorts that the closure will be phased over three years.

“At the very least this gives the workforce time to look for alternative employment and I understand that external consultants will be brought in to assist with this process.

“I also understand that the company will now start the process of offering early retirement, or even possibly relocation, but this is obviously a matter for the company to sort out with its staff members.

“Finally, we must not forget that nationally we have the lowest unemployment rate since 1975 and that Sudbury remains an attractive place to run a business.

“The responsibility going forward is for national and local stakeholders to come together to ensure that Sudbury has an even brighter future.”