Hilchos Lashon Hara chapter 8, section 8

. There is an opinion that one may speak lashon hara about baalei machlokes – people wrongfully quarreling with others. This only applies if one sees that by showing people their great dishonesty in this matter they will understand they are wrong and this will quiet the controversy. Without this, this case is no different. Also, the following conditions must be met:
a) One must know the facts indicating they are baalei machlokes personally and not rely on hearsay from others unless it is clear to one that it is true.
b) One must have the above benefit in mind and not speak because of hatred.
c) If one can quiet the controversy in some other way without speaking of them, such as by administering rebuke, one may not speak lashon hara about them. Sometimes one is afraid to rebuke such people lest, realizing that he is not on their side the baalei machlokes may circumvent his plan [to stop the quarrel] and leave him with no way to emend the situation. However, matters like these require great deliberation. A person should not be quick to decide which side of the quarrel involves baalei machlokes, but consider the situation according to Torah law. If he cannot decide, it is better to do nothing.