Union leaders today claimed that mobile phone giant O2 plans to make a further 400 workers redundant.
The cuts will mean the firm is axing up to 1,000 jobs after previously announced plans to cut 600, said the Communication Workers Union.
The jobs will be lost from call centres in Bury, Glasgow, Leeds and Preston Brook, near Warrington, said the union, which is already balloting its members in the company for strike action over outsourcing of work to Capita, job losses and job security.
The company has told staff that the original plans to cut 500-600 jobs on a voluntary basis will be at the top end of the scale with 600 people taking a package to leave by July 6, said the union.
In addition, the company announced that it will cut a further 400 jobs with people leaving by December. Remaining staff will be transferred to Capita in July, with up to 3,800 people affected by the outsourcing and redundancy plans, said the CWU.
Andy Kerr, CWU deputy general secretary, said: "We're dismayed and disappointed at this latest announcement of job cuts from O2 at such short notice. The outsourcing transfer date is less than three weeks away and the goalposts appear to be moving daily. This is not how a decent, responsible employer should behave.
"Our members in O2 have been brutally destabilised. They've been given a very short period to consider serious decisions about their future. Many don't know whether to stay or go, whether to take some money and leave now or take a chance on Capita.
"These job cuts will mean the permanent loss of decent jobs in these towns and cities. We remain gravely concerned for the future job and site security of people affected by outsourcing to Capita and we have further talks aimed at securing the best assurances we can for people's jobs, terms and conditions. We're urging all members to vote yes in the current ballot."
There was no immediate comment from the company.