Once upon a time when dinosaurs roamed on earth I worked at a hotel where we had a whole bunch of oil workers staying long term as they were there on a contract job. Quite a few of them would be the first ones in for breakfast, then head back to their rooms, come back in later with lunch packs and start packing their lunchboxes with items from the buffet.
We had words with them. They completely ignored us and carried on as usual. What they didn't know was that the father to one of the breakfast staff was their local boss. When it had gotten to a point that it was just getting to be too much (they were also quite abusive to the hotel bar staff in the evenings) they all got shipped back home and we couldn't have been happier.