More than 70 jobs are under threat at the Wyman Gordon mechanical parts factory in Livingston, says Unite Scotland.
The trade union said 72 of the 187 staff at the plant which supplies in Livingston had been issued with redundancy notices.
The plant makes components for the aerospace, oil & gas and nuclear industries. It makes engine parts for clients including Rolls-Royce, which is cutting 9000 jobs worldwide after a downturn in business from commercial airlines.
The factory was established as Cameron Iron Works by American owners in 1964 and its forged products division was bought by US firm Wyman Gordon in 1994.
Unite regional officer Graeme Turnbull said: "Unite will fight these proposed redundancies because this is an unnecessary decision by Wyman Gordon.
"We understand the challenges facing the sector but the company should continue using the job retention scheme while specific sector support packages are brought forward.
"More needs to be done by the UK and Scottish governments to stabilise those sectors who have borne the brunt of the Covid-19 pandemic."
