Legal reasons to not give reason for rent increase

[Paul M.]

Are there legal reasons not to give a reason for raising rent?   I can understand why there might be tenant relationship or business reasons why to do so not do so, but that is not what I'm talking about.   I often hear of rumors of legal reasons not to.  Certainly you don't want to give a reason that could be construed as retaliation for something the tenant did.    Are there other legal reasons?