There's probably no God.

That message has been the talk of the town in Canadian cities after an atheist group posted the sign on the side of several buses in Toronto and Calgary.

The sign, which also urges people to "stop worrying and enjoy their life" has caused an intense debate between religious groups and the Freethought Association of Canada, the organization who paid for the advertisements.

Some religious groups have even responded by putting up their own signs to counter the atheist ads but officials with Freethought say there's nothing offensive about their message.

"We're not going to be very careful around people like that, we're not going to walk on egg shells anymore because that's what atheists have done for centuries and that's not acceptable," Freethought president Justin Trottier said. "People are so set in their ways that they can't allow for the fact that there's an atheist organization in existence. That's their problem, not mine."

Trottier said the advertising campaign is a way to give atheists a voice.

"We're not after public money. We're after a seat at the table and access to public space, just like everybody else," he told CTV's Canada AM on Tuesday.

Trottier said the ads are meant to attract people who already don't believe a God exists, those that consider themselves atheist, agnostic or humanist.

"If they come from a position of skepticism and doubt, we want them to embrace that," he said. "Rethinking your beliefs can actually be very healthy in an open democracy like Canada."

He cited a recent poll, which found about 20 per cent of Canadians don't believe in a higher power.

Iman Syed Sohawardy, from the Islamic Supreme Council of Canada, said his group launched a counter campaign to present the public with a balanced perspective.

He told Canada AM that he's particularly concerned about young children who are just beginning to read and who are too innocent to think about the subject critically.

Sohawardy also said that the atheist ads have brought religious people closer to God by reminding them of their beliefs.

"It (tries to) show people who don't believe in God are less worried than those who do believe in God," he said. "But they are worried because they are not sure whether God exists or not. It means they're confused. We're not confused."