Right-to-work legislation prohibits unions and employers from entering into contractual agreements that require all employees to belong to a union or to pay union dues.  This type of legislation prevents union membership from being a condition of employment.  As of December 2012, there were 24 states in the United States that had passed right-to-work legislation. In Canada, right-to-work legislation would come into conflict with the Rand formula, which requires all workers to pay union dues when in effect. 

The Canadian Centre for Policy Alternatives gives a detailed history of efforts to introduce Right-to-Work legislation in Canada.