A Christian bus driver has refused to drive a bus with an atheist slogan proclaiming "There's probably no God".
Ron Heather, from Southampton, Hampshire, responded with "shock" and "horror" at the message and walked out of his shift on Saturday in protest.
First Bus said it would do everything in its power to ensure Mr Heather does not have to drive the buses.
Buses across Britain started displaying atheist messages in an advertising campaign launched earlier this month.
Mr Heather told BBC Radio Solent: "I was just about to board and there it was staring me in the face, my first reaction was shock horror.
"I felt that I could not drive that bus, I told my managers and they said they haven't got another one and I thought I better go home, so I did.
"I think it was the starkness of this advert which implied there was no God."
When he returned to work on Monday he was called into a meeting with managers and agreed to go back to work with the promise he would only have to drive the buses if there were no others available.
First Bus said in a statement: "As a company we understand Mr Heather's views regarding the atheist bus advert and we are doing what we can to accommodate his request not to drive the buses concerned."
It added: "As an organisation we don't endorse any of the products or sentiments advertised on our buses.
"The content of this advert has been approved by the Advertising Standards Agency and therefore it is capable of being posted on static sites or anywhere else."
The advertising campaign is backed by the British Humanist Association and prominent atheist, Professor Richard Dawkins.
Hanne Stinson, chief executive of the British Humanist Association, said: "I have difficulty understanding why people with particular religious beliefs find the expression of a different sort of beliefs to be offensive.
"I can't understand why some people seem to have a different attitude when it comes to atheists."
Pressure group Christian Voice has questioned the campaign's effectiveness but the Methodist Church said it would be a "good thing if it gets people to engage with the deepest questions of life" and suggested it showed there was a "continued interest in God".
The advertisements run on 200 bendy buses in London and 600 vehicles in England, Scotland and Wales.