There are cat bullies in many households. They are the alpha cat, the one who calls the shots and they do it in many ways. They simply stare, pounce on the other feline while he/she is sleeping, block entry ways I such as the cat door or sprawl out in doorways to other rooms, hiss and growl without motive, force another cat away from food or water bowls, squeeze in between owner and other cat when owner is holding the other cat or go out of their pathway to bump another feline just to remind them who the boss is. .
By nature cats are territorial and in terrains where there is more than one feline be in indoors or outdoors, a hierarchy is apt to develop. The biggest cat often, though not always, will dominate the top shelf of the social cat tree.
Make sure that you are not favoring one cat over another. Somehow cats sense this and there is a little jealousy involved in the bad behavior which can be easily corrected by you by merely giving Alpha Cat more attention and an extra treat now and then...
Other scenarios that can rouse bullying behavior in cats include having too many cats in too small of an area and/or having too few reserves. Many cat specialists will tell you that you should have at least one bowl of water, one bowl of food and one litter box for each feline. Some veterinarians advise having one extra, in particular in the case of litter boxes. Cats that have not been neutered/spayed or were fixed later in life have a tendency to be more naturally aggressive and territorial.
Keep in mind that freshly introduced cats do need to work out where each fits into the social hierarchy and this will certainly involve hissing, posturing, and staring until the all is settled. It may even rivet one major tooth and claw clash for the pair to learn who truly the governing cat is. If you interfere too often during this changeover, you will probably only extend this adjusting period which can cause even greater stress to you and your felines than if you just let them work it out by themselves. Some cats may never be friends, but others will bond beautifully in time