diff --git a/models/res_partner.py b/models/res_partner.py
index 7456b27..fe58603 100644
--- a/models/res_partner.py
+++ b/models/res_partner.py
@@ -18,3 +18,24 @@ class ResPartner(models.Model):
         # Add custom field for customer membership level
         fields_list.append('membership_level_id')
         return fields_list
+
+    def write(self, vals):
+        """
+        When a partner's membership level changes, delete their loyalty cards
+        from the OLD level's program so they don't accumulate cards across levels.
+        """
+        if 'membership_level_id' in vals:
+            new_level_id = vals['membership_level_id']
+            for partner in self:
+                old_level_id = partner.membership_level_id.id if partner.membership_level_id else False
+                # Only act when the level is actually changing to a different value
+                if old_level_id and old_level_id != new_level_id:
+                    old_cards = self.env['loyalty.card'].search([
+                        ('partner_id', '=', partner.id),
+                        ('program_id', '=', old_level_id),
+                    ])
+                    if old_cards:
+                        # Archive instead of delete — loyalty cards may be referenced
+                        # by pos_order_line.coupon_id (FK), so unlink() would fail.
+                        old_cards.write({'active': False})
+        return super().write(vals)