Here is what the Supreme Court of Canada said when it rendered its decision:

"The legislation deleted collective agreement terms between the applicant, the British Columbia Teachers’ Federation (BCTF) and the British Columbia Public School Employers’ Association (BCPSEA), the exclusive employer bargaining agent for the Province of British Columbia, the defendant. The legislation also prohibited future bargaining on certain issues."

If you believe that a legislative body should have the power to step in and, by way of legislation, amend a contract between and employer and the union duly certified to negotiate on behalf of that employer's workers, and further more to impose on both the union and the employer what they may or may not include in future contracts, you may want to look at the constitutions of China or Russia for inspiration on how to amend Canada's constitution.