British Steel producer Corus is due to end weeks of speculation by announcing thousands of job losses hitting several plants across the UK.
Last-ditch pleas by unions and politicians have been rejected by the company.
It blames restructuring on the strength of the pound, tough trading conditions and loss of traditional markets.
The huge factory at Llanwern near Newport in south Wales is expected to be hardest hit although other sites in Wales and Northern England are also expecting bad news.
Corus chairman, Sir Brian Moffat has come under strong pressure from ministers, MPs and union leaders in the past few weeks to scale back the job cuts.
Some MPs said Sir Brian appeared to be shocked at the heavy lobbying at a meeting earlier this week, but the last-ditch pleas have not persuaded him to change the restructuring plans.
The company, formed in 1999 through a merger of British Steel and Dutch firm Hoogovens, axed 4,500 jobs last year but signalled further cuts when its two chief executives suddenly resigned before Christmas.
Unions are sure to mount a campaign to try to save as many jobs as they can and the UK Government is likely to offer help to redundant steelworkers.