An arbitration clause contained in the condominium regulations, even where included in regulations drawn up by the original owner of the building, is contractual in nature since it affects the individual rights of the co-owners by restricting the constitutionally guaranteed right of access to judicial protection, and accordingly its amendment or repeal requires the unanimous consent of all co-owners, a majority resolution of the assembly under Article 1136 of the Civil Code being insufficient, on pain of nullity of the resolution under Article 1138(4) of the Civil Code.