The CIRB's mandate is to contribute to and promote effective industrial relations in any work, undertaking or business that falls within the authority of the Parliament of Canada. It interprets and applies the Code in a manner that supports and promotes free collective bargaining and the constructive settlement of disputes.

Under the Code, the Board has jurisdiction in regard to some 800,000 employees and their employers engaged in federal jurisdiction industries, which include interprovincial transportation (air, land and water), broadcasting, banking, longshoring and grain handling, to some Crown corporations, and to private-sector employers and employees in Nunavut, the Yukon, and the Northwest Territories.

In general, Part I of the Canada Labour Code charges the Board with a twofold responsibility: that of granting, modifying and terminating bargaining rights, and that of resolving, through mediation or adjudication, complaints of unfair labour practice concerning violations of the Code by trade unions or employers.

Under Part II of the Code, the Board must rule on complaints by employees alleging that they have been discriminated against or punished for exercising their rights in relation to safety.

On finding a violation of the Code, the Board is empowered to order reinstatement and compensation where appropriate. It is also empowered, upon application, to order employees to return to work in cases of illegal work stoppages and to attempt to resolve or adjudicate, where necessary, various other types of disputes that may arise under Part I of the Code.