I have heard it said that one can only use one each of any particular Unique or LE in a Battleforce for tournament purposes. For example you could not use two Mikel Nova Cats in a tournament battle but you could use both Mikel and Kym Nova Cat in a tournament Battleforce. I have looked through the rules but can't find anything about this. Can someone clarify this for me?
Thanks

You cannot use two of the same unique in the same force. But, you can use a unique to fight the same unique in another force. (one Mikel in your force fights another in a another force) Just because they have the same last name doesn't mean they are the same unique.

Thanks for the help. Can you provide a reference where this is stated in the rules or FAQ?

ROW (Rules of Warfare, the rulebook) page 6

"Your battleforce may contain two or more of the same unit, unless that unit is unique.
A unit is unique if it has a star on its base as a rank symbol. It’s okay if the same unique unit appears in opposing battleforces on the same battlefield."

Also note, that's going by the collector's number on the base. There are two pieces with the name Jaquelin Pejiko (ROTS LE Crane & Liao Tian-zong).