This is usually a act of dominance if it is a male cat. If it is a female cat you might want to get him/her checked at your vet for a urinary track infection. This is very common in cats.
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My cat has not yet been spaded...She is a year old and showing signs of being in heat. She now has started to urinate on my bed. Why is she doing this?
Well in all male animals cats have the ability to scent anything they want to, to let animals know that it is their territory and they have been there maybe your cat is trying to tell you that the beds are his and there is only one other way besides keeping the doors shut and that is to take him to the vet and get the vet to do his thing if you know what i mean.
Maybe you didn't train it where it should go to urinate, it doesn't know where to go to urinate.