P.R. Laws Ap. tit. 32A, § III, Rule 63.1
A judge, whether on his own initiative or on motion of party, shall disqualify himself from an action or proceeding in any of the following cases:
(a) When he is interested in the outcome thereof, has personal bias against, or is partial to any of the parties or their attorneys.
(b) When he is related by blood or affinity within the fourth degree to any of the parties or their attorneys.
(c) When he has been attorney or counsel for any of the parties or their attorneys in the action pending before him, or prosecuting attorney in an investigation or criminal proceeding wherein the facts are the same as those to be submitted to him for decision.
(d) When a friendship exists between the judge and any of the parties or their attorneys, of such nature as to thwart the ends of justice.
(e) When there is any other cause that may reasonably cast doubt upon his impartiality to adjudicate or which tends to undermine the public confidence in the administration of justice.