The 15-member court voted 10-4 in favor of the Philippines' military accord with the US, court spokesman Theodore Te told journalists on Tuesday.
"EDCA is not constitutionally infirm… As an executive agreement, it remains consistent with existing laws and treaties that it purports to implement," he said,
In doing so, the judges rejected a petition by some lawmakers and activists to declare the country's Enhanced Defense Cooperation Agreement (EDCA) with the US unconstitutional because it surrendered the Philippines' sovereignty to a foreign country.
The EDCA was signed in 2014 but not implemented due to legal challenges. An approval of the accord meant there would be more US troops in the country for war games and military exercises.
Dozens of anti-US activists held protests outside the court saying the ruling was "untenable" and would make the Philippines "a launching pad for military intervention in the region."
Manila and Washington to discuss strategies
The decision comes hours before Manila's officials speak to their US counterparts to address security concerns arising from Beijing's increasing presence in the South China Sea.
Department of Foreign Affairs spokesman Charles Jose said the Philippines would ask the US to continue patrols and ensure that commercial and military ships pass easily in the area. Officials were also discussing the possibility of patrols together with other Asian allies of the US.
Countries bordering the South China Sea are worried that Beijing could impose an air defense identification zone (ADIZ) after it recently tested a runway on an artificial island called the Fiery Cross. "They can declare it officially or we may witness a de facto ADIZ," Jose told the media.
Beijing stakes claim on a vast part of the South and the East China seas, whose islands are believed to have huge reserves of oil, gas and rare minerals. In 2013, it declared an aviation security zone in the East China Sea, where it has been contesting with Japan over the possession of uninhabited islands.
mg/rc (AP, AFP, Reuters)