When you are disabled and applying for short term disability you are making an insurance claim. Your rights are found in your short term insurance policy.
Generally your employer has very little to do with your Short Term Disability STD (STD). You’ll be dealing with an insurance adjuster when you are receiving or apply for Short Term Disability.
If you belong to a union your employer has obligations it must comply with when you are disabled and applying for Short Term Disability. These obligations are contained in the collective agreement.
Your rights will be found in the insurance policy. Each policy is different. Read your insurance policy over in detail, if you still have any questions or concerns I suggest you contact a lawyer.