Or "hearing by a limited bench" – whatever suits your context in terms of grammar. I think this term is, however, little-known in the Anglophone world, do I might be tempted to say intstead:

hearing before/by a limited bench (of three judges) or
hearing before/by a panel of three judges or

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Here's a reference, from the website of the Cour de Cassation:

Cette formation, en vertu d ’une loi du 23 avril 1997, est composée de trois magistrats lorsque la solution du pourvoi s’impose, quel qu’en soit le sens (rejet, cassation, irrecevabilité et non admission). Dans le cas contraire, elle doit comprendre au moins cinq magistrats ayant voix délibérative. On emploie souvent les termes de « formation restreinte » dans le premier cas, de « formation de section », dans le second.
http://www.courdecassation.fr/institution_1/savoir_plus_inst...

Pursuant to an Act of 23 April 1997, a bench comprised of three judges is necessary to rule on a case for which the outcome of the appeal is obvious notwithstanding the actual decision of the Court (dismissal, quashing of the lower court’s decision, non-admissibility and non-admission). Otherwise, the bench must be comprised of at least five judges who are entitled to vote. The term “limited bench” is used for the former and “section bench” for the latter.
http://www.courdecassation.fr/about_the_court_9256.html


And here's an example, in a decision:
Holds that a new hearing will be held before a limited bench (of three judges on 13 December 2011;
http://www.google.com/url?sa=t&rct=j&q="limited bench" franc...
(good luck: very complicated URL)



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Note added at 1 hr (2012-07-22 20:25:30 GMT)
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Typos:
• "so I might be tempted to say instead..."
• close parenthesis dropped after "of three judges" in the last reference
:o

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Note added at 1 hr (2012-07-22 20:26:48 GMT)
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• extraneous "or"
:o :o

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Note added at 4 hrs (2012-07-22 23:38:05 GMT)
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I found a simpler URL for the translated decision:
http://www.veron.com/publications/Decisions\20110722\2011-05...

Plus, I just found the decision in the original French:
Dit que le présent dossier sera rappelé à l'audience de formation restreinte di 13 décembre 2011 ;
http://www.veron.com/publications/Decisions\20110722\2011-05...

So Véron & Associés also felt the need to add "of three judges" to their translation. ;-)



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Note added at 4 hrs (2012-07-22 23:39:08 GMT)
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Sorry, another typo: "du 13 décembre 2011."