Tata Steel is to cut 250 jobs and mothball a plant at one of its sites, according to sources.

The jobs are understood to be being cut in South Wales, mainly at Llanwern, which is set to have some of its mills mothballed.

It is believed that the job losses will involve agency workers.

Dave Hulse, national officer of the GMB union, said: "This is more bad news for the steel industry. This comes on the back of the recent announcement that 720 jobs will go in the Speciality Business.

"The 250 jobs to go will be drawn from agency workers who are currently employed at Tata Steel sites.

"There are genuine and well-founded concerns over the future of the steel industry in the UK. GMB will propose that the Trades Unions Steel Committee write to Prime Minister David Cameron requesting a meeting to discuss these concerns over the long-term future.

"We will see local communities destroyed with mass unemployment while the balance of payment deficit will increase further if we don't act now and get Government support and action.

"Energy-intensive industries need access to affordable and secure energy. Government must ensure competitive tariffs for large-scale power users so that the push for low carbon does not drive heavy industry out of the UK.

"Unless Government acts, what's left of the steel industry will be at risk."

Roy Rickhuss, general secretary of Community and chairman of the National Trade Union Steel Co-ordinating Committee, said: "We fully acknowledge that Tata Steel, and indeed the entire UK steel industry, is under huge pressure to reduce costs and become sustainable. Cripplingly high energy costs combined with the strength of the pound and a flood of Chinese imports are killing the industry and we desperately need Government to stand up for steel and make a game-changing intervention.

"However it is extremely regretful that most of those to be laid-off are highly motivated and committed young people, currently employed through an agency but who hoped to pursue a career within Tata Steel.

"It's tragic that these young people, who have been trained up by Tata and in normal circumstances would be considered the future of the business, are being let go in the drive to cut costs and remain competitive in the global marketplace."