An employee shall be allowed one (1) day off to attend the funeral or other bereavement rite of a sister-in-law, spouse’s grandparent or a brother-in-law. Reimbursement for this day shall be the same as provided below.
-Article 29 Section 2 of the 2018-2023 National Master Agreement
They just added the spouse’s grandparents in the new contract. You might want to check your supplement to see if you’d be covered under the old one. Regardless, I’d take the day and talk to the steward and center manager about it. They should be able to give you funeral pay. If not, file a grievance to have it added to your retro check.