The Government is being urged to consider nationalising Liberty Steel in a bid to save thousands of jobs.
The company has asked ministers for £170 million in financial support to pay operating expenses and deal with recent losses.
Concerns over the future of the steel maker have been expressed after financial backer, Greensill Capital, went bust.
Liberty Steel employs around 5,000 workers at a number of sites across the UK.
Unite’s assistant general secretary Steve Turner said steel was a foundation industry and was essential for the recovery of the UK economy from Covid-19.
“This is key to protecting the jobs of its workforce and the communities where it is based, to safeguard its supply chain and ensure its customers receive the products they require.
“No option should be ruled out in protecting the long-term future of Liberty Steel, and that must include the option of nationalising the business.
“The loss of Liberty Steel and the specialist products it manufacturers for the aerospace, automotive and oil and gas sectors would have damaging consequences beyond the steel sector itself.
“While the loss of the thousands of skilled, well-paid, unionised jobs it provides is unthinkable, deskilling whole communities, ripping hope of a secure job from future generations and damaging regional economies in areas of the country where unemployment is already high and wage rates are below average.”
A Government spokesman said: “The Government is closely monitoring developments around Liberty Steel and continues to engage closely with the company, the broader UK steel industry and trade unions.
“The Government has supported the steel sector extensively, including providing over £500m in recent years to help with the costs of energy.
“Our unprecedented package of Covid support is still available to the sector to protect jobs and ensure that producers have the right support during this challenging time.”
It is understood that ministers have concerns about the structure of the company and whether any bailout would remain in the UK.