The Philippine government is refusing to yield in a territorial standoff with China. Braving threats of retaliation, Manila lodged its legal case with a United Nations tribunal on Sunday, challenging Beijing’s sovereignty claims in the South China Sea and raising the stakes in a longstanding dispute.

Beijing immediately dismissed the move, saying it would refuse to take part in any arbitration by the International Tribunal on the Law of the Sea.

Manila’s decision to lodge nearly 4,000 pages of legal testimony with the tribunal in Hamburg “is about defending what is legitimately ours,” Philippines Foreign Secretary Albert del Rosario told reporters in Manila on Sunday.

The Philippines has been the most outspoken of the Southeast Asian nations that have competing claims with China in the South China Sea. Beijing lays claim to more than 80 percent of the sea, thought to be rich in oil and gas, within nine dotted lines shown on a Chinese map drawn up in the 1940s.

Within that tongue-shaped area lie reefs and shoals more than 1,000 miles from China’s shoreline.

Chinese and Philippine vessels have clashed near disputed islets in the South China Sea where both countries claim ownership. On Saturday, a civilian Philippine boat evaded two Chinese coast guard vessels in order to resupply soldiers stationed on Second Thomas Shoal.

China has ignored the Philippines’ bid for international arbitration, first opened a year ago. Beijing says that it announced in 2006 that it would not submit to arbitration procedures under the UN Convention on the Law of the Sea in sovereignty disputes.

As soon as the Philippines announced its new legal move on Sunday, Chinese Foreign Ministry spokesman Hong Lei condemned Manila’s “illegal occupation of some of China’s islands and reefs” and urged the Philippines to “return to the right track of settling the disputes through bilateral negotiations.”

The Southeast Asian nations at odds with China over territories in the South China Sea – Vietnam, Brunei, Malaysia and the Philippines – fear that in any bilateral talks, each would be vulnerable to economic and political pressure from its giant neighbor. They prefer a multilateral approach, which China has consistently rejected.

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Beijing has made no secret of its readiness to punish Manila for its diplomatic and legal campaign. “As a close neighbor and trading partner of Beijing, Manila has a big stake in the smooth development of their bilateral ties, to which a wise return to the negotiation table is crucial,” warned a commentary published Monday by the state-run Xinhua news agency.

In 2012, during a dispute over fishing rights, the Chinese government temporarily halted the import of bananas from the Philippines, ostensibly on food safety grounds. Beijing later lifted the ban, but the spat ended with a Chinese coast guard vessel on permanent station near the disputed Scarborough Shoal, just 120 miles west of the Philippine island of Luzon.