Why does my younger rabbit keep peeing on my older rabbit?

They usually do this to mark their territory! Although it is usually the older rabbit that is more territorial...

Hi jedward.fan13 here...I have a rabbit who is 3 years old and recently I adopted a baby rabbit, but the baby rabbit seems to keep peeing on the older one, Do you think this might be because the baby rabbit hasn't been spayed yet and the older one has?