Short answer. Yes. Under Article 114 of the Revised Penal Code, a Filipino citizen commits treason by levying war against the Philippines or giving aid or comfort to her enemies, whether within the Philippines or elsewhere, so it reaches acts done abroad. The penalty is reclusion perpetua to death, though RA 9346 (2006) bars the death penalty.
What the law says
Any Filipino citizen who levies war against the Philippines or adheres to her enemies, giving them aid or comfort within the Philippines or elsewhere
Revised Penal Code, Article 114 — Treason Against The Philippines. Read the full provision →
What treason is
Treason is the gravest betrayal of one's own country. Article 114 of the Revised Penal Code defines it as one of two acts by Any Filipino citizen who levies war against the Philippines or adheres to her enemies, giving them aid or comfort. The first way, levying war, means taking up arms or joining an armed uprising against the state. The second, adhering to the enemy while giving aid or comfort, means siding with a hostile power and actually helping it, whether by supplying information, resources, or support. Loyalty in thought alone is not enough; there must be an overt act of help.
Can it be committed abroad?
Yes. The article says the aid or comfort may be given within the Philippines or elsewhere. That last word is deliberate: treason is one of the few crimes that follows the Filipino citizen beyond the country's borders. A citizen who helps an enemy of the Philippines from another country is just as answerable as one who does so at home. The duty of loyalty is treated as personal to the citizen, not tied to where he happens to stand. The article also reaches an alien, residing in the Philippines, who commits the same act, because a resident alien owes a temporary allegiance too.
The penalty today
The article states the penalty as reclusion perpetua to death for a citizen, plus a fine. That text must be read against later law. Republic Act 9346 (2006) prohibits the death penalty in the Philippines, so death can no longer be imposed; in its place the law imposes reclusion perpetua. The fine figures in the article, which run to millions of pesos, come from Republic Act 10951 (2017), the law that updated the money amounts throughout the Code. For a resident alien the article sets a slightly lower range, reclusion temporal to death, likewise read subject to the death-penalty ban.
The strict proof treason requires
Treason carries an unusually strict rule of proof, a safeguard against false accusations of disloyalty. The article provides that No person shall be convicted of treason unless on the testimony of two (2) witnesses at least to the same overt act or on confession of the accused in open court. So a conviction cannot rest on one witness, on rumor, or on a confession made privately or under pressure outside court. Two witnesses must point to the very same treasonous act, or the accused must own it before the judge. This makes treason one of the hardest crimes to prove, by design.