Without a union, the terms of your employment depend on your contract with your employer. In most situations, an employer can fire an employee for no reason at all, as long as they give proper notice or severance pay. Depending on what province you're in, the amount of time you should get for notice/severance will vary, but a reasonable average is one week per year that you worked for the employer.
A smart employer will not give any reason for firing an employee, because once they give you a reason, you may have grounds for a wrongful dismissal law suit, or a Human Rights case. In your situation, it doesn't so much matter whether you actually have a disability. If your employer is treating you as though you are unable to do the work, or as though they suspect you are disabled, then that counts as discrimination. There is also some variation from province to province, but most provinces Human Rights Codes specify that in cases of discrimination on the basis of disability, whether or not the employee is disabled does not matter. The only thing that matters is if the employer is acting as though they think the employee is unfit.
So you have two main options:
- if your employer did not give you notice/severance pay, you can complain to the local Labour Board. The result is usually that you get the pay owed to you.
- if you think there might be wrongful dismissal or discrimination, either because you were away on sick leave, or because your employer thinks that you can't do a good job anymore, then you would need to talk to an employment lawyer (or paralegal, in Ontario) who can help you through the process of filing a claim.
It is probably a good idea to talk to a lawyer/paralegal to help making that decision, as they can tell you more about what each option might cost, and which option is more likely to give you a better award if you're successful.
To find a lawyer who will give you an initial half hour consultation at no charge, you can contact your local law society. They usually have a referral service that will connect you to a lawyer who practices in the type of law you need. If you would prefer to give me information on where you work/live (city, province) I could check that information for you.
I hope I have fully answered your question, but please do not hesitate to ask for more information if needed. When you are satisfied with the answer, kindly provide me a positive rating so I can receive credit for my answer.
My answer here contains only general legal information and not legal advice. No solicitor/client relationship has been created by this communication.