TAGUIG CITY — Former Supreme Court Associate Justice Antonio Carpio on Tuesday urged the government to file a formal protest against China's declaration under the High Seas Treaty within the year, warning that failure to do so could be interpreted as consent to Beijing's maritime claims.

“In my opinion, we should protest within one year, because there are cases where you can protest within two years,” Carpio said, stressing the need for a timely response.

China ratified the High Seas Treaty in 2025, formally known as the Agreement on Biodiversity Beyond National Jurisdiction (BBNJ) under the United Nations Convention on the Law of the Sea (UNCLOS).

The treaty, which took effect on 17 January 2026, seeks to ensure the conservation and sustainable use of marine biodiversity in areas beyond national jurisdiction.

Carpio noted that China issued a declaration in December 2025 that, in his view, requires a formal counter-declaration from the Philippines.

“We have to make a counter-declaration,” Carpio said.

“The High Seas treaty applies to the South China Sea. The Philippines must start it [filing], because if we don't, we will have impliedly consented to China's claim, and we will lose a maritime zone, our exclusive economic zone,” he added.

During a forum organized by the Stratbase Institute and the French Embassy in Manila on high seas governance in Taguig City, Carpio explained that the treaty aims to protect biodiversity in the high seas through the creation of marine protected areas, environmental impact assessments and mechanisms for sharing marine genetic resources.

He noted that while oceans cover 71% of the Earth's surface, about 64% of the ocean surface consists of high seas, equivalent to roughly 45% of the planet's total surface area.

China's claim

Carpio said the dispute stems from China's 2009 submission to the United Nations asserting sovereign rights and jurisdiction over waters, seabed and subsoil within its so-called nine-dash line claim. In 2020, China's map expanded the claim to a 10-dash line, which Beijing treats as an international boundary.

“What is enclosed by your boundary is your national territory,” Carpio said.

“China has ramped up and doubled down on its claim. This would violate UNCLOS because, [under] Article 89, no state may subject any part of the high seas to its sovereignty,” he added.

Carpio warned that if China's interpretation prevails, neighboring countries such as Vietnam and Brunei could lose access to maritime zones currently recognized under international law.

He said he is currently urging the Department of Foreign Affairs to file a counter-declaration as soon as possible.

“That means we impliedly consent, tacitly agree to the claim of China,” he said of the consequences of failing to act.