Steel giant Tata is cutting 900 jobs and closing 12 sites under plans to improve competitiveness.
Tata said most of the job losses will be in South Wales, including 500 at the Port Talbot plant, under restructuring of management and administrative posts.
A total of 580 jobs will be cut in Wales, 155 in Yorkshire, 120 in the West Midlands and 30 on Teesside.
Sites to close include Tafarnaubach and Cross Keys in South Wales, while shift levels at the company's Rotherham and Hartlepool plants will be reduced to match production to lower demand for bar products and pipelines.
Indian-owned Tata Steel also announced that it will re-start one of two blast furnaces at Port Talbot in the first quarter of next year as part of a £250 million investment programme.
Karl Kohler, chief executive of Tata Steel's European operations, said: "These restructuring proposals will help make our business more successful and sustainable, but the job losses are regrettable and I know this will be a difficult and unsettling time for the employees and their families affected."
"We will do everything we can to reduce the impact of the proposals on employees and, where possible, we will look to achieve job losses through voluntary redundancies," he added.
Michael Leahy, general secretary of the Community trade union, said: "This news will be of great concern to many of our members and their families.
"We will be seeking an urgent meeting with the company to ensure our principle of no compulsory redundancies is upheld, although we are pleased to see the company has already committed to offering a package of training and support for those affected by these changes."
A Welsh Government spokesman said: "This is very disappointing news, and a massive blow to those who will be losing their jobs. The Welsh Government has a very strong relationship with the company and officials will now work with Tata to establish a task force and identify what support we can provide for those affected."