A Christian bus driver from Southampton, Hampshire, has objected to driving a bus with a slogan proclaiming ‘There’s probably no God – now stop worrying and enjoy your life’.
Mr Ron Heather says he is "shocked" and 'horrified" at the message and walked out of his weekend shift in protest.
The company involved, First Bus, said that it would seek to accommodate his feelings - but an advertising agency worker told Ekklesia: "religious advertising has been around for years, and non-religious people haven't boycotted it, even if they have objected."
Buses across Britain started displaying the "probably no God" messages in an advertising campaign launched earlier this month by the British Humanist Association and others.
Commentators have suggested that the wording is closer to agnosticism than atheism.
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.
He continued: "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."
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."
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."
The advertisements run on 200 bendy buses in London and 600 vehicles in England, Scotland and Wales.
Christian Voice activist Stephen Green, whose past activities have been roundly condemned by church leaders and other Christian groups, is trying to get the ASA to ban the advert.
The Methodist Church and other religious people have welcomed the advert as part of public debate and communications.
Simon Barrow of the religion and society think-tank Ekklesia commented: "The reality is that we now live in a mixed-belief society, and Christians and others are going to need to get used to this. Being offended that other people think differently to you achieves nothing. We need to learn to talk and listen to one another better."
He added: "The larger issue in all this is the way that beliefs, religious and otherwise, are increasingly being 'commodified' in a consumer culture - sold like products. But what convinces people of the value of a way of life or belief is its fruit in good lives, not an endless endless cycle of propaganda and anti-propaganda."
"Given the suffering, conflict and injustice in the world, one would hope that people of faith and people of general good will would want to find common purpose through investing in humanitarian causes rather spending a vast amount of money sloganeering," said Barrow.