My first questions are, is it an obstruction of a potential fire exit? And is anyone concerned about it’s presence? If the answer to 1 is yes, politely tell them to move it.
If the answer to 2 is also yes, I feel pretty sure you’ll have a by-law about not leaving goods on, or obstructing, common property without written permission.
That’s all the legislation you need and in any case there’s unlikely to be any other laws specifically about this kind of thing although there may be local council fire regulations.