BT has announced it is set to close its Sheffield base - but the firm has promised no workers will lose their jobs as a result of the move.
The telecoms company is moving out of Telephone House, in Charter Square in the city centre, as the lease is due to expire.
Around 400 BT workers and agency staff work at the high-rise 15-floor tower, from where Sheffield’s phone network has been controlled for nearly 40 years.
Kirsty Lenham, Sheffield and district branch secretary for the Communication Workers’ Union, said: “We’re helping our members with this process and are hoping to keep as many jobs a possible in Sheffield.
“It’s a real blow to workers in Sheffield, some of whom have over 40 years service with BT and some are understandably upset.”
BT staff could move out of the premises as early as September this year.
A spokesman for BT said the lease ends in 2013, and the landlord is already marketing the building for sale.
“We are committed to finding the best options now for all our people working in the building, to ensure they remain employed by us,” he said, adding alternative jobs will be available in business sales in Sheffield and consumer sales in Doncaster.
Staff can also take up roles with BT’s sister company Plusnet in Sheffield, or working from home.
“We have briefed our people and asked them for their views on these options,” the spokesman said.
Telephone House was built on the site of old council houses and completed in 1972.