Final answer:
WHMIS symbols are required on both supplier and workplace labels in Canada. However, international trade rules do not mandate all nations to impose the same consumer safety standards, as countries can set their own, albeit with a duty to communicate and negotiate on these standards for international trade purposes.
Step-by-step explanation:
The Workplace Hazardous Materials Information System (WHMIS) is Canada's national hazard communication standard. The key elements of the system, including the hazard classification criteria, cautionary labelling requirements, the provision of safety data sheets (SDSs), and worker education and training programs, require WHMIS symbols on both supplier and workplace labels. While WHMIS symbols are mandatory in Canada, the rules of international trade do not necessarily require that all nations impose the same consumer safety standards, including the use of these symbols. Instead, international trade rules generally allow countries to set their own safety standards, but they must inform trading partners and negotiate any differences that could affect trade.