Strikes and lock-outs are economic sanctions that parties impose upon each other during a collective bargaining dispute.

Although they vary from jurisdiction to jurisdiction, there are several statutory conditions which must be met before the parties can exercise their right to strike or lockout.

Every jurisdiction makes it unlawful for the employer to lock out, or the employees to strike, during the operation of a collective agreement. Strike deadlines are set by each Province’s labour legislation. In Ontario, the union must hold an employee vote prior to declaring a strike is in effect.

Although the definition varies between Provinces, essentially any concerted activity by employees designed to restrict or limit output in order to force the employer to make concessions at the bargaining table is a strike. A strike may be found to occur even where the concerted activity consists of failing to perform voluntary duties. For example, if all of an employer’s employees refuse to work voluntary overtime, an illegal strike may exist.

It is also unlawful for any person or trade union to counsel, call or authorize an unlawful strike or do anything the reasonable and probable result of which is to cause an unlawful strike.

Every employee has the right to engage in a lawful strike or, alternatively, to continue to work if the employer permits employees to cross the picket line. Employees may lawfully picket the employer's business while on public property so long as the picketing does not illegally restrict ingress or egress from the employer's premises. In most jurisdictions, the employer's remedy for picketing which goes beyond the communication of information is an injunction application to the courts. Certain preconditions must be met before an injunction will be awarded. In Ontario, for example, there are three such preconditions. Before an injunction will be issued, an employer is required to demonstrate:

1. direct evidence of illegal conduct on the part of picketers (this could include blocking company-required vehicles from entering or exiting or delaying them for an excessive period of time, violence or assault on the picket line, harassment, property damage, etc.);
2. that police assistance has been unsuccessful in preventing or controlling the illegal picketing; and
3. that the illegal picketing will cause irreparable harm to the employer.

At one time, it was held that it was unlawful for employees to engage in secondary picketing; that is, picketing by employees of a business not connected to or allied with the employer. Secondary picketing would occur when employees picketed suppliers of their employer in order to exert pressure on their employer to resolve collective bargaining impasses. However, in RWDSU, Local 558 v. Pepsi-Cola Canada Beverages (West) Ltd. [1998] S.C.C.A. No. 624, the Supreme Court of Canada held that secondary picketing was legal, so long as the actions of the picketers did not constitute a separately actionable wrong (i.e. criminal or tortuous conduct). The Supreme Court held that picketing, secondary or otherwise, was a form of expression that must receive Constitutional protections so long as it was otherwise legal.