Don’t know if you were being facetious or not, but, as I have no knowledge of legal terms, I looked up “no sua sponte en banc”. Here is what I found.
En Banc(1.):
(In the bench. Full bench.) Refers to a session where the entire membership of the court will participate in the decision rather than the regular quorum. When the issues involved are unusually novel or of wide impact, the case will be heard and decided by the full court sitting en banc.
Sua sponte (1.):
Of his or its own will or motion; voluntarily; without prompting or suggestion.
Source: http://clarit.home.mindspring.com/glossary.htm#e
To be honest, I wasn’t joking. You had me accepting those words as authentic. Hah. Some people (like me) are easily mystified when it comes to knowing the law.