A review of bus operations in Norfolk threatens more than 100 jobs, a union is warning.
Stagecoach has launched a consultation over the potential closure of its depot in King's Lynn, which runs around 50 vehicles and employs 120 staff, in response to the "challenging economic environment".
The firm said a combination of rising operational costs and pressure on public budgets had affected investment in buses.
Andy Campbell, managing director of Stagecoach East, said: "We are a significant local employer and we understand the importance of bus services for the local community.
"We also know that any change can be unsettling for our people. That's why we are working closely with both the trade union and local authority to protect as many jobs and as much of the local network as possible.
"We're carrying out a consultation and will be liaising closely with staff during that process, however the reality is that we simply cannot sustain the current operation given the challenging economic climate that we're faced with."
A spokesman for Norfolk County Council said: "It's disappointing that Stagecoach have come to the conclusion that they can no longer operate sustainably in West Norfolk and we are sorry to hear this news.
"However, we will work as closely as we can with them to ensure passengers are kept informed of changes and the network is covered by alternative providers as much as possible."
Rail, Maritime and Transport union leader Mick Cash said: "RMT officials are in urgent discussions with Stagecoach after this bombshell announcement which leaves jobs and services in Norfolk hanging by a thread.
"Stagecoach has only operated Norfolk bus services since December 2013 and serious questions need to be asked as to exactly what has gone wrong and why.
"In the wake of the Carillion collapse, here we have yet another example of what happens when privatisation and profit is allowed to take priority over public service.
"Bus services are already being slashed and axed across the country as private operators cherry-pick the profitable routes."