The South China Sea Code as a test of ASEAN’s agency

15 April 2026

The South China Sea Code of Conduct (COC) has returned to the diplomatic forefront, propelled by the Philippines’ 2026 ASEAN chairmanship and the familiar rhetoric of urgency: momentum, acceleration, and deadlines. At the ASEAN Foreign Ministers’ Retreat held on 29 January 2026 in Cebu City, foreign ministers reiterated their ambition to establish an effective and substantive code consistent with international law, particularly the United Nations Convention on the Law of the Sea (UNCLOS). Meanwhile, China continues to attend ASEAN meetings and endorse the goal of concluding negotiations.

Yet Southeast Asia should resist the tendency to treat the COC as a finish line. The code is neither a sovereignty settlement nor a mechanism capable of reconciling incompatible territorial claims. Rather, it is a stress test of ASEAN’s cohesion and its capacity to convert institutional habits into meaningful restraint — in a maritime space where power asymmetries persist and coercion is often calibrated to remain below the threshold of open conflict.

ASEAN’s influence has rarely depended on hard power. Instead, it has rested on its ability to shape regional habits through institution-building and diplomatic convening. While this institutional logic remains intact, its limits are repeatedly tested on the South China Sea.

ASEAN must therefore navigate internal diversity and external pressure simultaneously. Internally, member states remain divided between claimants and non-claimants, divisions that have at times constrained the bloc’s ability to adopt collective positions. Externally, China continues to combine diplomatic leverage with coercive actions at sea, this includes repeated water-cannon incidents against Philippine vessels near Second Thomas Shoal in 2024.

Ultimately, the COC’s relevance will depend on whether it can institutionalise guardrails that shape incentives at sea, reduce the frequency and severity of grey-zone encounters, and make de-escalation after incidents more predictable.

The COC can be understood as three negotiations happening at the same time. ASEAN is negotiating with China, but it is also negotiating internally on how much its members are willing to compromise to adopt common positions. At the same time, ASEAN must consider how much legal principles can realistically influence behaviour in an environment defined by strategic rivalry. On the South China Sea, ASEAN centrality therefore depends on bargaining power, shaped by uneven interests and threat perceptions within ASEAN, as well as the wider asymmetry of power with China.

ASEAN’s constraints on the COC

The COC process unfolds under two structural constraints: internal divisions within ASEAN and external power asymmetry vis-à-vis China. Together, these constraints narrow the range of outcomes that are politically acceptable and operationally meaningful.

The first constraint is shaped by ASEAN’s uneven stakes in the South China Sea. The Philippines, Vietnam, Malaysia, and Brunei Darussalam are partial claimants over maritime features and adjacent zones that overlap with — and are contested by — China’s claims. While Indonesia is not a territorial claimant, China’s expansive maritime narrative intersects with Indonesia’s lawful entitlements around Natuna, a friction Jakarta treats as a matter of jurisdiction under UNCLOS rather than territorial bargaining. Other ASEAN members are not claimants and may perceive the South China Sea less as an urgent security threat and more as a diplomatic issue to be managed without disrupting economic ties with China.

These varying stakes within the bloc limit the degree of cohesion that ASEAN can sustain in negotiations. As a consensus-based organisation, unity is often preserved through language that all members can accept, but this often results in diluted outcomes. Two cases illustrate how these internal divisions operate: at the ASEAN Ministerial Meeting in 2012, Cambodia’s blocking of the joint communiqué prevented a collective statement altogether; in 2016, consensus was preserved but only at the cost of substance, producing a statement that avoided any direct reference to the arbitral ruling. The muted response in 2016 demonstrated how internal divisions can weaken collective positions, while the 2012 failure illustrated how these divisions can collapse consensus entirely.

The second constraint is more structural. Negotiations over a binding, operational code are ultimately negotiations over constraints on behaviour. As the strongest actor in the South China Sea, China has little strategic incentive to accept strict limits when the balance of power at sea works in its favour. Manila’s insistence that the code be grounded in UNCLOS and legally binding is therefore understandable. Without a firm legal baseline, the COC risks repeating the limitations of the 2002 Declaration on the Conduct of Parties signed by ASEAN states and China, which provided a political framework for self-restraint and peaceful dispute management, but lacked enforceable commitments to constrain coercive conduct at sea.

Bindingness is therefore not a semantic debate but the heart of negotiations. Binding language implies accountability; accountability implies costs; and costs imply limits on behaviour. Stronger actors tend to prefer flexibility and interpretive room, while weaker actors prefer clarity and rules that protect them. The eventual shape of the COC will therefore reflect not only legal principles, but also the balance of power that determines how much restraint stronger actors are willing to accept and how much protection weaker parties are able to secure. On the South China Sea, the legal debate is inseparable from the strategic one.

What can the COC realistically deliver?

Expecting the COC to serve as a sovereignty treaty is unrealistic as sovereignty is what is being contested. The more realistic and urgent function of the code is narrower but still significant. It can act as a behavioural guardrail that reduces miscalculation and limits routine incidents that risk escalation, including dangerous manoeuvres, confrontations between coast guards, harassment of fishing fleets, and grey-zone tactics. Without-prejudice clauses could protect sovereignty positions while still being specific enough to make restraint operational rather than merely rhetorical.

A thin COC is attractive: it can be announced as progress, cited as evidence that diplomacy works, and used to reduce reputational costs for all parties. It may even modestly lower the risk of accidental escalation. Yet thinness carries political consequences. A code that stabilises dialogue without constraining coercion risks normalising asymmetry: ASEAN maintains the diplomatic process, while China retains its strategic advantage.

A thick COC, by contrast, would include precise commitments governing operational conduct at sea: de-escalation procedures, rapid consultation and incident communication mechanisms, and enforceable rules on unsafe manoeuvres, coast guard conduct, and obstruction of lawful maritime activities. That remains difficult for three reasons. First, ASEAN’s consensus structure complicates agreement on hard clauses when member states face unequal risks and diverging threat perceptions. Second, China has limited strategic incentive to accept provisions that would reduce the effectiveness of grey-zone coercion or increase the attribution of violations. Third, repeated confrontations at sea reduce the trust and narrow the political space needed for stronger commitments. Under such conditions, deadlines often produce ambiguity rather than discipline, rewarding diplomatic closure even when the conditions for meaningful operational restraint remain absent.

Indonesia’s “third position” and measuring COC success

Indonesia’s position illustrates the broader ASEAN dilemma. Observers often seek simple labels — neutral or claimant — but Indonesia occupies a third position. Under President Prabowo Subianto, Indonesia has sought to preserve ASEAN cohesion, sustain the negotiation process, and maintain workable relations with Beijing, while holding a firm legal line on maritime jurisdiction around Natuna. This is not inherently contradictory. However, in contested waters, signalling carries legal and strategic weight, and ambiguity can be exploited.

The controversy surrounding the wording of overlapping claims in the 2024 China-Indonesia joint statement demonstrated how quickly diplomatic language can be read as concession, despite Jakarta’s subsequent reaffirmation that it does not recognise China’s expansive South China Sea claims. The lesson for the COC process is clear: wording is never merely cosmetic but carries legal and strategic consequences. Ambiguous formulations can shape expectations, blur legal positions, and give stronger actors room to translate diplomatic flexibility into strategic advantage.

The lesson applies directly to the COC’s operational core: behavioural provisions are only meaningful if they make violations attributable, politically visible, and diplomatically contestable. Their value lies not in hard enforcement, which remains unlikely in an asymmetric environment, but in creating shared procedures that increase the reputational and political costs of non-compliance, enable faster crisis communication, and provide ASEAN members with a clearer basis for collective signalling when agreed rules are ignored. Such mechanisms would not eliminate coercion, but they could narrow the space in which coercion operates without diplomatic consequence.

Ultimately, the COC’s relevance will depend on whether it can institutionalise guardrails that shape incentives at sea, reduce the frequency and severity of grey-zone encounters, and make de-escalation after incidents more predictable. This is precisely where the ASEAN dilemma becomes most acute: a code thin enough to preserve consensus may do little to restrain coercive conduct, while a more demanding code may prove politically difficult if some members see its provisions as constraining their own security cooperation, external engagement, or energy partnerships more than they do China’s behaviour.

The South China Sea dispute will not be solved by paper alone. But the right kind of text, designed as a guardrail rather than a trophy, can still matter, precisely because the alternative is a maritime arena in which escalation becomes routine and miscalculation is only a matter of time.

DISCLAIMER: All views expressed are those of the writers and do not necessarily represent those of the 9DASHLINE.com platform.

Author biography

Dr. Aniello Iannone is a lecturer in Indonesian and Southeast Asian Politics at the Department of Political Science and Government, Diponegoro University. His research focuses on Indonesian politics, ASEAN as a regional actor, and comparative and international politics in Southeast Asia. Image credit: David MacSweeney.