Walmart is demanding a physical copy of my PGWP even though I’ve already submitted my IRCC work authorization letter. Is this legal?

Hi everyone,
I’m wondering if anyone else has experienced this.
I recently received my IRCC work authorization letter and submitted it to Walmart as proof that I’m authorized to work in Canada. However, my store is insisting that I also provide a physical copy of my Post-Graduation Work Permit (PGWP) before they will process everything.
As far as I understand, the IRCC work authorization letter allows me to continue working while my work permit is being processed. So I’m confused about why they’re refusing to accept it on its own.
Has this happened at your Walmart store as well?
Did your HR or People Lead ask for the physical PGWP?
Were they willing to accept the IRCC work authorization letter instead?
How did you deal with the situation?
I’m just trying to understand whether this is a company-wide policy, a store-specific requirement, or if anyone has successfully resolved a similar issue.