First West of England is currently running 90 per cent of its services compared to before the pandemic but with a third fewer passengers.
Managing director Doug Claringbold said government funding has helped the industry to break even but without it the challenges are unsustainable.
Speaking on BBC Radio Bristol on January 17, he said: “If the funding isn’t there we’re going to have to take a hard look at the services we operate because it’s unsustainable to run 90 per cent of the services with 63 per cent of the fare box.
“This is a really serious moment in terms of the bus industry.
“The West of England Combined Authority is supporting services throughout the region. We have a significant challenge. We’re lobbying hard, as is the combined authority and loads of MPs to get support for the network beyond April.”
First has announced a raft of changes from January 30, with services being axed, reduced or rerouted.
The 37 bus route between Bath and Bristol via Hanham and Longwell Green is among those being withdrawn from January 30.
In Portishead, the X3, X3a and X4 services will be replaced with an amended version of the X4, which will not operate via Marina after continued issues with parked vehicles causing delays over a number of years.
Mr Claringbold said he was “deeply apologetic” to those who are inconvenienced by the changes.
He added: “We’ve targeted a number of changes in January. Part of the changes are to significantly improve the reliability of our network.
“We’re preparing plans – if there’s no funding or further support we will have no choice but to make more significant changes to the network.
“We’re working to achieve the best network for customers. Take the 37 – just because a service has operated that way for many years doesn’t mean that it should continue in its current format.
“People are making different journey choices. We have to respond to what the current needs are.
“What’s really optimistic is the commitment to spend money on infrastructure around buses.”