Telecoms giant NTL announced plans today to cut its workforce by 6,000 following its recent merger with rival Telewest.
The company said more than a third of its 17,000 staff will be affected by the upheaval, which is likely to involve up to 1,000 compulsory redundancies.
NTL said a number of jobs will be transferred under outsourcing agreements, including 1,500 to IBM.
Amicus national officer Peter Skyte said: "This is a devastating blow for thousands of employees across the whole country. There is no corporate social responsibility in this announcement and it is difficult to fathom how cutting so many UK jobs will be good for NTL's customers."
Gerry Morrissey, assistant general secretary of Bectu, said his union will now press for a campaign to highlight the number of jobs being outsourced to India.
"Firms which are doing this don't deserve the support of the British public," he said.
NTL said the 6,000 jobs will be cut by the end of next year as it looks to save £250 million through its merger with Telewest in March.
The tie-up with Telewest created the largest provider of residential broadband services in the UK and was followed by the acquisition of Virgin Mobile, making it the first operator with a "fourplay" offer of pay TV, internet access, fixed-line telephone and mobile calls.
NTL has radically reshaped itself since emerging from bankruptcy protection in 2003, beginning with a major financial overhaul to generate new capital and reduce interest repayment charges.
It organised a rights issue to raise £824.3 million and trimmed its workforce, with 1,500 call centre staff losing their jobs in cuts announced two years ago.
Today's news is a fresh blow to British industry after mobile phone giant Orange announced plans last week to axe up to 2,000 jobs under a review of its operational costs.
Rival telecoms firm Cable & Wireless warned in February that it may reduce its 5,500-strong UK workforce to between 2,500 and 3,500 over the next four to five years.
NTL chief executive Steve Burch said the merger with Telewest was "progressing well" and said the company planned to "accelerate" the process.
Mr Burch said: "Part of this process will involve outsourcing a significant number of jobs, where employment would be transferred to an external organisation, as well as actual job reductions.
"In total, this will involve around 6,000 employees by the end of 2007. Around 80% of the reduction will take place within 12 months."
Employees at the NTL office in Bellshill, outside Glasgow, remained silent about the job loss announcement this morning.
Workers seen leaving and entering the main reception area said "no comment" to waiting members of the press.
It was not yet known how many, if any, of the 900 employees are affected by the merger.