Up to 100 staff from Bristol and Somerset who work in administrative roles with bus operator First Bus have been told their jobs are at risk.
Drivers and maintenance staff were not affected by the move which the company said was due to tough economic times.
"Decisions which affect the workforce are always difficult to make. We deeply regret any uncertainty the situation causes," a First spokesman said.
A 30-day consultation period with staff and unions has now started.
"In tough economic times we, like many other businesses across the county, have to ensure we are operating as efficiently as we are able to.
"The move is about seeking efficiencies in back office operations in our business which covers Bristol, Bath, Taunton, Weston-super-Mare, Wells and Yeovil," the spokesman added.