I would say that if the harbour or marina is privately owned they can do what they want. Certainly I've heard of boats being refused entry into marinas in the Med during a storm. In the Balearics in July/Aug there are far more boats at anchor than could possibly be accomodated in harbours and marinas. Personally, I've been towed out of a marina in Ibiza against my wishes when I could'nt start my engines and been unceremoniously dumped outside so I could well imagine the same marina refusing entry to incoming boats in a storm