MANILA — Manila can rally an "overwhelming majority" of allies against Beijing if it raises before the United Nations an arbitral ruling that invalidated China's claims over the West Philippine Sea, retired Supreme Court Associate Justice Antonio Carpio said Monday.

President Rodrigo Duterte's administration has refused to do so over fears that China can demand the support of countries to which it gave economic aid, he said.

However, the Philippines has the backing of the US, UK and Australia which gave “much, much more than what China has given to other countries.”

"Once we get the support of these other countries, the big powers, I think we will get an overwhelming majority in the General Assembly," he told ANC.

Duterte previously shelved the 2016 arbitral award as he pursued loans and investments from Beijing. However, the President last week told the UN General Assembly that the Philippines "firmly rejects" any attempt to undermine the ruling.

The UN is the “locus” and “moral force” of world opinion, Carpio said, adding that smaller countries previously won against more powerful counterparts before the UN, as in the case of Nicaragua against the US, Mauritius against the UK, and the Netherlands against Russia.

"This will happen to China if we play it right... The other countries are just waiting for us to move," he said.

"China needs the world to survive. It needs to export, import...It wants to be a leader in the world. But how can you be a leader if you do not follow international law?"

The entire foreign affairs department, including all Philippine ambassadors, will have to campaign to get the votes against China, which has no veto power in the UN General Assembly. The campaign may take 2 to 3 years, he said.

In the meantime, the Philippines can "fortify" the ruling by citing it and filing for an "extended continental shelf claim" facing the South China Sea, the same way that Vietnam and Malaysia did, said Carpio.

"We don’t need the consent of any state, we don’t need the consent of China to file that. That affirms that we have an exclusive economic zone in the West Philippine Sea," he said.

The Philippines can also enter into a convention with Vietnam and Malaysia, and invite the US, France, Britain, Australia and Japan, Carpio suggested.

The convention should affirm the ruling by stating that in the Spratly Islands, "there is only territorial seas and beyond those seas will be the Exclusive Economic Zone" of the Philippines, that will uphold freedom of navigation and flight, he said.

-- With a report from Jamaine Punzalan, ABS-CBN News