British Columbia Transit violated rights to free speech when it refused to carry political ads on the outside of its buses, the Supreme Court of Canada has ruled.

The unanimous 8-0 ruling is a victory for the Canadian Federation of Students and the British Columbia Teachers' Federation, two groups that tried to place ads on the outside of B.C. buses in the run-up to the provincial election in 2005.

Grace Pastine, litigation director for the B.C. Civil Liberties Association, said BC Transit and TransLink now have no choice but to change their policy of only allowing commercial advertising.

"If TransLink continues to allow other types of advertising — continues to allow commercial advertising on the sides of buses — then they must also allow political advertising. That is, it's not for them to decide what is political and what is commercial, and to allow one but not the other."

Pastine called the court victory an important win in the fight to preserve free speech.

TransLink spokesman Ken Hardie said the decision finally clarifies the ground rules for the company.

"What we wanted was to basically canvass the issue as thoroughly as possible, Hardie said Friday. "We still have, probably, the same options that would be available to any advertising medium to look at the appropriateness of advertising — political or otherwise — and to accept or reject advertising based on established critieria that has been out there for many years."

Hardie said TransLink will follow those guidelines, which are set down by the Canadian Advertising Standards Council, which he says gives the company flexibility in what advertising it does accept.

The ads in dispute raised several issues, including tuition fees, the environment and school closures.

BC Transit had refused to run them, saying its policy bans political ads along with any message "likely to cause offence … or create controversy."

With files from The Canadian Press