This pro-atheist ads on a British bus says: 'There's probably no God. Now stop worrying and enjoy your life.' (AP)

A 'Without God' ad has proven too controversial for Halifax transit.

Humanist Canada wanted to place ads on Metro Transit buses with the slogan, "You can be good without God."

But officials with the transit authority deemed that too controversial.

"We're a public transit system first, and then we sell advertising," Lori Patterson, spokewoman for Metro Transit, told CBC News on Monday.

"So, if anytime we feel there's a message that could be controversial and upsetting to people, we don't necessarily sell the ads."

That decision is upsetting to Pat O'Brien, president of the non-profit group dedicated to the separation of church and state.

"It would be interesting to see what vegans think about the KFC ads. I mean, at what point do you stop offending people?" he said.

The group hopes to buy ads in Toronto and Vancouver.

"Our ad has been shown to be acceptable to everyone else in the country," said O'Brien. "Some people like it, some don't. That's fine. It's all about getting the message out and getting the conversation going."

A slightly different message has been splashed on buses in London, England. Various groups and individuals paid for atheism-promoting slogans like, "There's probably no God. Now stop worrying and enjoy your life."

Patterson said the transit authority would reconsider its position if Humanist Canada toned down its message.

But O'Brien said that won't happen.