P.R. Laws Ap. tit. 32A, § III, Rule 20.3
(a) As soon as practicable after the commencement of an action brought as a class action, the court shall determine by order whether it is to be so maintained. An order under this subdivision may be conditional, and may be altered or amended before the decision on the merits.
(b) In any class action maintained under Rule 20.2(c), the court shall direct to the members of the class the best notice practicable under the circumstances, including individual notice to all members who can be identified through reasonable effort, except when this would be so difficult as to obstruct the prosecution of the action, in which case the court shall determine the manner in which notice shall be given. The notice shall advise each member that:
(1) The court will exclude him from the class if he so requests by a specified date;
(2) the judgment, whether favorable or not, will include all members who do not request exclusion; and
(3) any member who does not request exclusion may, if he desires, enter an appearance through his counsel.
(c) The judgment in an action maintained as a class action under Rule 20.2(a) or (b), whether or not favorable to the class, shall include and describe those whom the court finds to be members of the class. The judgment in an action maintained as a class action under Rule 20.2(c), whether or not favorable to the class, shall include and specify or describe those to whom the notice provided in Rule 20.3 (b) was directed, and who have not requested exclusion, and whom the court finds to be members of the class.
(d) When appropriate, an action may be brought or maintained as a class action with respect to particular issues, or a class may be divided into subclasses and each subclass treated as a class, and the provisions of this rule shall then be construed and applied accordingly.