Mobile phone company T-Mobile is to cut some 800 jobs at sites across the UK.
The losses are part of a restructuring by parent company Deutsche Telekom which will see a total of 2,200 jobs lost across Europe.
Of the jobs to go in the UK, T-Mobile told Personnel Today that about 500 would be redundancies and the rest would go through outsourcing.
The job cuts will hit major sites at Hatfield, Hertfordshire, Sunbury, Surrey, Merthyr Tydfyl, Pembrokeshire, Doxford, Northumberland, Greenock, Renfrewshire, Warrington and Solihull. There are also a network of retail outlets across the UK that will be severely effected.
Communication Workers Union organiser Nick Childs said the announcement would come as an enormous blow to working members at T-Mobile.
"They are the ones who have stuck by the company through thick and thin. Now the company is repaying their loyalty and hard work by throwing one in eight of staff on the dole," Childs said.
"The union will be doing everything in its power to support and back its members to protect their jobs. As always we would like to do this in a grown up way through mutually beneficial negotiations with management however, we will not hesitate in our duty to our members in taking further action if this becomes necessary."
However, a T-Mobile spokeswoman said the company's market model had to change as it was now operating in a saturated market. She said the group hoped to make savings of £1bn through the restructuring.