DICCIONARIO DE TERMINOLOGfA
]URfDICA MEXICANA Javier E Becerra

contrato social - articles of association, articles of
incorporation, partnership agreement: las
relaciones internas de las sociedades irregulares
se regiran por el -- -- respectivo y, en su defecto,
por las disposiciones de Ia Ley General de
Sociedades Mercantiles I the internal
relationships of irregular corporations shall be
governed by the corporation's own articles of
incorporation and, in the absence thereat by the
provisions of the General Corporation and
Partnership Law.

"Contrato Social" "articles of incorporation" http://tiny.cc/bxasiw

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Note added at 10 mins (2012-08-09 18:27:24 GMT)
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As pointed out in the misspelled version of this quesiton by Allegro at http://www.proz.com/kudoz/spanish_to_english/law_general/490...
"exact term will depend on the structure of the entity concerned- asker needs to be aware"

Therefore, "partnership agreement" is a possibility as show in the above dictionary reference