Soon after the decision, the union instructed its members to remove the signatures.
They were changed from the company's trademark “Building trust. Driving confidence," to "We work, you drive; we both deserve better.''
ICBC says the changed signature has hurt the corporation's brand and its lawyer contends the messages are a tactic for employees to garner sympathy for the union.
The lawyer representing the union argued that the signatures are a form of job action, and are no different from picketing or distributing leaflets.
ICBC and the union have been locked in a labour dispute since 2010, and while union members passed a strike vote in June, the Labour Relations Board ruled they couldn't stage a full-scale walkout.