We would need more context - say, is it a litigious action? if it were, it would be a Power ad Litem

I definitely agree with José. In order to give a correct answer we would need more context.
Refs.:
http://esl.proz.com/kudoz/spanish_to_english/law_general/189...
"...es lo mismo que un poder para pleitos, o mandato judicial.
S/Cabanelas también: agency for judicial matters, power of attorney pertaining thereto..."

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Note added at 11 hrs (2010-01-09 03:09:59 GMT)
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SORRY!!!!!!
Instead of "Special" I meant LIMITED. But then again, we need more context.

A Limited Power of Attorney is an important legal document that allows or authorizes the person you name (your Agent, "attorney-in-fact") to perform a particular transaction. The Limited Power of Attorney would restrict the authority of the Agent to a specific situation, limited time period or type of legal action. A Limited POA is also referred to as a "Special" Power of Attorney and can be either Springing or Durable.

****A Durable Limited Power of Attorney (Specific or Special POA) is an important legal document that allows or authorizes the person you name (your Agent, "attorney-in-fact") to perform a particular transaction. The Limited Durable Power of Attorney restricts the authority of the Agent to a specific situation, limited time period, or type of legal action.

****A Non-Durable Limited Power of Attorney (Specific or Special POA) is an important legal document that allows or authorizes the person you name (your Agent, "attorney-in-fact") to perform a particular transaction. The Limited Non-Durable Power of Attorney would restrict the authority of the Agent to a specific situation, limited time period or type of legal action.

REF.: http://www.legalhelpmate.com/power-of-attorney.aspx

conferimos poder especial judicial, cuanto en derecho se requiere a los abogados en ejercicio...

we grant limited power of attorney, when the law requires the lawyers to excerise...

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Note added at 1 day2 hrs (2010-01-09 17:16:20 GMT)
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in this instance it is a limited power of attorney because your friend only requires the lawyers for a specific action, it is not a generalised power of attorney.