Niether the airline or anyone else is allowed to go through your luggage without you being present unless they have a warrant. We always use the plastic cable ties on our baggage. It won't stop a real thief but at least we will know right away if someone has been in there and make an immediate complaint.
If the ties were cut or tampered with I would immediatly call ships security, the Hotel Manager and Purser and let them all know and demand an explaination. This should not occur. I get very touchy with someone going through my personal possessions!