Tata Steel has confirmed that it will cut 1,200 jobs at its plant in Scunthorpe and Lanarkshire.
Around 900 of the cuts will come at Scunthorpe, which is one of the UK's largest steel plants and employs 4,000 people. The remaining job cuts will come at its Lanarkshire plant.
It comes just weeks after 1,700 workers lost their jobs at the SSI Redcar plant. Last week, there was a summit between unions, steel firms and government in which the unions demanded greater support for the industry.
The UK's steel industry blames much cheaper imports from China for the slowdown, something that the Prime Minister will address during the state visit of China's President this week.
Indian-owned Tata has scaled back its operations over the past year due to falling steel prices and the strength of the pound, which has impacted on exports.
John Park, assistant general secretary of trade union Community, warned of the impact it could have on the steel industry in Scotland. He said: "The significance of this is that it could be the end of steel production in Scotland.
"Tata Steel have to be persuaded to mothball the site rather than close it and the Scottish government has to have a role in keeping the infrastructure secure and supporting short-time work until a future can be secured."
David Cameron said: "The British government is doing everything that we can, and every issue that we can take up, we will."