Communications giant Virgin Media is to to close a call centre over the next 18 months which union leaders said could lead to the loss of 500 jobs.
The firm said staff at the site in Trowbridge, Wiltshire will be given the chance to redeploy or take voluntary redundancy.
The Communication Workers Union said the decision was a "disaster" for the local area following a move by Vodafone last month to close its centre on the same site, with the loss of up to 200 jobs.
Andy Kerr, deputy general secretary of the CWU, said: "This is a disaster for Virgin Media staff at Trowbridge and for the whole area. Coming on the back of the Vodafone decision to pull out of Trowbridge, the local economy will be hit hard by this redundancy double whammy.
"We're asking Virgin Media to make redeployment and relocation packages a realistic option for staff who may be interested, not a token tick box exercise. The sad fact is that there will not be an option to stay in Trowbridge and work for Virgin Media as other sites are not within commuting distance and relocation remains an unrealistic option for the majority of staff.
"The closure will be phased over 18 months, but this is no consolation for staff, many of whom have long service for the company, who ultimately face losing their job."