A small group of protesters demonstrated outside Halifax City Hall Tuesday to show their opposition to Metro Transit's decision not to place atheism-themed ads on its buses.

"Shame on Metro Transit for such obvious discrimination," Justin Trottier, president of the Freethought Association of Canada, said at the rally. "If the human rights commissions weren't busy themselves trying to censor words and images, they might look into our case, a genuine and obvious example of atheist discrimination."

About 16 protesters stood with Trottier, complete with bright orange duct tape on their mouths and holding two signs. One sign read "This is what metro transit is protecting you from." The second sign showed the now-infamous ad that was declined by Metro Transit: "There's probably no God. Now stop worrying and enjoy your life."

That slogan first appeared on buses in London, England, as part of an ad campaign promoting atheism that has since been duplicated in one form or another in other parts of the world.

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

But officials with the transit authority deemed that too controversial as well.

The protesters Tuesday branded Metro Transit's refusal to advertise atheism-themed ads as "censorship."

Derek Rodgers, also with the Freethought Association, said his group is considering all options, including legal action.

"A number of litigators have come to us and expressed their support and offered their services," Rodgers said. "We haven't made any official decisions yet. That depends on what Metro Transit decides. The ball is in their court."

Meanwhile, a representative with Metro Transit told CBC News the city transit system is waiting for a supreme court decision on a similar dispute about bus ads in British Columbia before it reconsiders running the ads.