What to do next
Get the decision letter and the reason in writing
The letter states the ground relied on and the appeal deadline. Those deadlines are strict and are the most common reason valid claims fail. Request your complete claim file at the same time - you are generally entitled to it, and it shows what the board actually considered.
Address the specific ground
Where causation is disputed, the answer is medical evidence connecting the injury to the work. Where a pre-existing condition is cited, the question is usually whether work aggravated it - aggravation is generally compensable even where the underlying condition was not caused by work.
Build the evidence the board did not have
A supportive report from your treating physician addressing work causation specifically, witness statements from colleagues, incident reports, and a description of the physical demands of your job. Reports that address causation directly carry far more weight than clinical notes.
Understand the appeal levels
Most systems have an internal review followed by an independent appeals tribunal - WSIAT in Ontario, WCAT in British Columbia and Alberta, the TAT in Quebec for CNESST matters. Each level has its own deadline and its own standard.
Know what you cannot do
Workers compensation is generally a no-fault system that bars suing your employer for the injury. Claims against a negligent third party who is not your employer may remain available, and are worth assessing separately.
Frequently asked questions
Can I sue my employer instead?
Generally no - the system is no-fault and bars most claims against the employer. A claim against a negligent third party may still be available.
They say my condition is pre-existing.
Aggravation of a pre-existing condition by work is generally compensable. The medical evidence needs to address aggravation specifically rather than the underlying condition.
I reported the injury late.
Late reporting is a common ground for denial but not always fatal - explain the delay and provide corroborating evidence of when the injury occurred.
Do I need a lawyer?
Many jurisdictions provide free worker advisers or advocates, and they handle a great many appeals successfully. A lawyer is worth considering for complex causation or a significant permanent impairment.
Which tribunal hears the appeal?
WSIAT in Ontario, WCAT in British Columbia and Alberta, the Tribunal administratif du travail in Quebec. Each has its own page here with its process.
This is general information, not legal advice. Laws vary by location and every situation is different — speak with a qualified lawyer about your specific circumstances.