Ontario's four major teachers' unions said Thursday they are launching charter challenges to a law capping public sector wage increases, arguing it violates their collective bargaining rights.

Here are some other recent examples of labour groups across the country taking governments to court:

January 2018: The union representing Ontario's college faculty members files a charter challenge of legislation that ended a five-week strike and allowed 500,000 students to return to class. The president of the Ontario Public Service Employees Union says the back-to-work legislation introduced by Kathleen Wynne's Liberal government and supported by the Opposition Progressive Conservatives, violates workers' rights.

August 2017: The Nova Scotia Government and General Employees Union, the largest public-sector labour group in the province, launches a court challenge of provincial Bill 148. The legislation imposed a wage pattern on 75,000 public sector workers, among other measures. The challenge asked the province's Supreme Court to rule the entire bill unconstitutional, saying the government violated union members' rights to freedom of association and freedom of expression.

August 2016: Ontario Superior Court strikes down a 2011 back-to-work bill that sent striking Canada Post workers back on the job. The bill, passed by Stephen Harper's federal Conservative government, was challenged by the Canadian Union of Postal Workers. The court ruling backed the labour group by saying the law was unconstitutional.

April 2016: Ontario Superior Court sides with several major provincial education and public-service unions, ruling a 2012 Liberal bill legislating teachers back to work substantially interfered with their collective bargaining rights and violated the Charter of Rights and Freedoms.

April 2015: Citing a Supreme Court of Canada decision months earlier, an Alberta judge rules that sections of the province's Public Service Employees Relations Act were unconstitutional. In doing so, the judge upholds a challenge from the Alberta Federation of Labour.

January 2015: The Supreme Court of Canada strikes down a Saskatchewan law that prevented public-sector employees from going on strike. By a 5-2 majority, the high court granted an appeal by the Saskatchewan Federation of Labour of the province's controversial essential services law that restricts who can strike.

March 2012: The Air Canada Pilots Association launches a charter challenge against back-to-work legislation passed by the federal government earlier in the month.

April 2011: The Supreme Court of Canada upholds an Ontario law preventing the province's farm workers from unionizing. The high court decided that the province's existing Agriculture Employees Protection Act gives workers a meaningful process by which to bargain. It allows farm workers to join associations, but does not force employers to enter into collective bargaining. The challenge was mounted by the United Food and Commercial Workers Canada.