Can the management company of the building I live in say what we can or can't have in our patio?

I live in an apartment building with my family. Recently, my parents (and every other resident in the building) received a letter stating that if we did not remove items like brooms or towels from our patio's we would be fined $150. Though I think the fine's outrageous, I can see why they wouldn't want stuff like that uglyifying the building but they're not allowing birdhouses or plants or bikes either! We own our apartment, are they allowed to do this?