Labour Standards
Former employers are not legally obligated to provide a reference, or a reference letter.
In fact, your former employer is free to provide a bad reference, so long as the former employer believes it is true. If your employer makes untrue statements which hurt your job prospects, then you may be able to sue. However, these types of claims can be difficult to prove.
If you suspect that your employer would not provide a good reference, you may ask a more reliable supervisor or manager who you think would provide a better reference. There is no legal requirement that your employment references come from a direct manager.
Additionally, if you sue your employer for wrongful dismissal, you can include an agreement to provide a reference letter and/or a good reference as part of the settlement.