Employer managing STD? [AB Gov Union Position]

I was told to take medical (stress) leave by my doctor and when I went to submit my prescription, my employer informed me that they’re moving toward (not yet policy) with handling short-term disability claims going forward instead of our insurer- sun life. Is this allowed? The form that they are requiring me to fill in for my doctor allows consent for medical information and to me is very invasive, specifically questions about my ability to lead and such as a supervisor, the employer-created form seems very catered to my particular issues.

I was also informed that if I do not submit this form by next week I will be unpaid for the current leave (4 days) and forward - since I have a medical exception that would mean I cannot return to work and I wouldn’t be paid until the end of that time frame(?).

"I wanted to reach out as we have not yet received the functional information we require for your ongoing medical leave.

In my last email, I had requested you provide that documentation by August 20, 2026 – I appreciate the update you provided letting me know you were waiting for the doctor’s response. That being said, we do require functional information and I wanted to notify you that you will have until August 28, 2026 end of day to provide functional information otherwise you may go unpaid as of August 29, 2026".