OTTAWA -- The city might not be able to legally justify its refusal to run ads promoting atheism on city buses, the city solicitor says.

The Sun has obtained a confidential memo solicitor Rick O'Connor sent to councillors yesterday that says the decision might violate the Charter of Rights and Freedoms.

The Freethought Association of Canada recently applied to purchase advertising space on OC Transpo buses but was refused because its message -- "There's Probably No God. Now Stop Worrying and Enjoy Your Life" -- was found to contravene a city policy.

The policy says "religious advertising which promotes a specific ideology, ethic, point of view, policy or action, which in the opinion of the city might be deemed prejudicial to other religious groups or offensive to users of the transit system is not permitted."

Transit officials made the decision after receiving four complaints from the public.

"Based on the information available at this time, it appears that the city may not be able to justify its refusal of the proposed advertising on the basis that it is offensive, and consequently, it may be found to be an unreasonable infringement of the association's freedom of expression under Section 2(b) of the Charter," the memo says.

"If the decision to refuse the ads was based solely on the four complaints received from the public, it is likely that this decision will be found to be unreasonable and lacking in proportionality, and therefore not justifiable under Section 1 of the Charter."

Without more evidence the ads would be offensive to a reasonable number of transit users, O'Connor says it would be difficult for the city to successfully defend its decision in court if a challenge were to be filed.

Three weeks ago the city's transit committee voted to uphold OC Transpo's decision to reject the controversial proposed ads.

Council is expected to debate the issue today.