Tata Steel is expected to confirm plans to press ahead with plans to close both blast furnaces at its biggest UK plant, threatening more than 3,000 job losses.
Most of the job losses will be at Port Talbot in south Wales, which will have a huge impact on the local economy.
The company is expected to give details on Friday of when the jobs will be lost.
Unions have criticised the decision after the company rejected alternative plans they put forward on Thursday.
Steelworkers will be consulted in the coming weeks on how to respond, with industrial action not being ruled out.
Tata is planning to move to producing steel in a more environmentally friendly way using electric arc furnaces instead of blast furnaces which needs fewer workers.
Unions have warned of the “devastating” impact on jobs in South Wales as well as the future of the steel industry.
Community assistant general secretary Alasdair McDiarmid said: “We continue to believe the multi union plan is the best strategy for Tata Steel UK and can avoid compulsory redundancies, protect our steelmaking production capacity, and safeguard the future of Port Talbot and the downstream plants.”
A UK Government spokesperson said: “We are determined to secure a sustainable and competitive future for the UK steel sector, which is why we have committed £500 million of UK Government support that will transform the site and protect thousands of jobs, both in Port Talbot and throughout the supply chain.”
Unite has warned it will “use everything in its armoury” to fight job losses, including its £30 million strike fund.