If the pergola is on common property (as opposed to lot property) it doesn’t belong to you and so the strata can remove it if an EC or AGM votes to do so by a simple majority vote. They can also charge you for any costs involved in removeing the pergola if you refuse.
Are you sure it is on common property, have a look at the plans for when you bought the property which should show lot property and common property.
Also check the bylaws to make sure their is not an exclusive use bylaw referring to the pergola.