P.R. Laws tit. 31, § 3 : ONE Civil Code —Subtitle Preliminary Subtitle Preliminary Provisions —Chapter 1. The Laws, Their Effects, and the General Rules for Their Application —§ 3. Retroactive effect

Laws shall not have a retroactive effect unless they expressly so decree.

In no case shall the retroactive effect of a law operate to the prejudice of rights acquired under previous legislative action.