Short answer. As a rule, yes. Article 5 of the Civil Code says acts executed against the provisions of mandatory or prohibitory laws shall be void — with one exception: when the law itself authorizes their validity. So an act that breaks such a law is generally without legal effect unless the law making the rule saves it.
What the law says
Acts executed against the provisions of mandatory or prohibitory laws shall be void, except when the law itself authorizes their validity.
Civil Code, Article 5 — Acts Against Mandatory or Prohibitory Laws Are Void. Read the full provision →
What mandatory and prohibitory laws are
Article 5 speaks of two kinds of law. A mandatory law commands that something be done in a particular way; a prohibitory law forbids something outright. Both are the opposite of merely directory or permissive rules, which guide without invalidating what departs from them. The distinction matters because Article 5 attaches its severe consequence only to acts that run against the mandatory or prohibitory kind. When a rule truly commands or forbids, the law treats obedience as essential — not optional — so an act that defies it is not just irregular but, as a rule, stripped of legal effect altogether.
The general consequence: the act is void
The core of the article is blunt: acts executed against such laws shall be void. Void means the act produces no legal effect from the start — it is not merely voidable at someone's option, and it cannot be ratified into validity. A contract, waiver, or arrangement that contravenes a mandatory or prohibitory statute therefore gives rise to no enforceable rights; a party cannot sue to compel performance of it, and courts will not lend their aid to enforce it. This is the law's way of ensuring that a rule it considered important enough to command or forbid cannot be quietly defeated by private agreement to the contrary.
The exception the article builds in
Article 5 is not absolute. It ends with except when the law itself authorizes their validity. The lawmaker who lays down a mandatory or prohibitory rule may also decide that a violation should carry a consequence other than nullity — a penalty, for instance, while leaving the act itself effective, or a right in one party to have it annulled rather than treating it as void from the outset. Where a statute expressly provides such an alternative, that provision controls, and the act is not automatically void. So the answer is never purely mechanical: you must read the specific law that was broken to see whether it authorizes the act's validity.
Why "automatically" needs care
Because of that exception, calling every violation "automatically void" oversimplifies. Whether an act is void, merely voidable, or valid-but-penalised depends on how the particular statute treats the breach, and that can turn on subtle wording. Article 5 also does not tell you the further effects of nullity — what must be returned, whether a party in bad faith can recover, or how third parties are affected — which are governed by other provisions. So if you are relying on, or resisting, a deal that may collide with a mandatory or prohibitory law, the safe step is to have the specific law examined rather than assume the outcome.
Cases citing this provision
These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.
- Platon and Librada Ceruila vs. Rosilyn Delantar, et al, G.R. No. 140305, December 9, 2005 — read the decision on LawPhil →
- Energy Development Corporation vs. Commissioner of Internal Revenue, G.R. No. 203367, March 17, 2021 — read the decision on LawPhil →
- Commissioner of Internal Revenue vs. Team Sual Corporation (formerly Mirant Sual Corporation), G.R. No. 194105, February 5, 2014 — read the decision on LawPhil →
- Philippine National Bank, substituted by Tranche 1 (SPV-AMC), Inc. vs. Rina Parayno Lim and Puerto Azul Land, Inc, G.R. No. 171677, January 30, 2013 — read the decision on LawPhil →