When pollution crosses borders, sovereignty becomes more complicated. Singapore can suffer the consequences of fires burning in Indonesia, yet it cannot simply send investigators into Indonesian territory. Its attempt to hold companies accountable through domestic law has exposed a deeper dilemma in Southeast Asia: how can a region built on territorial sovereignty govern economic activities whose environmental costs routinely cross national boundaries?

In October, Singapore escalated its response to the region’s recurring haze crisis. The National Environment Agency issued preventive notices to 10 Indonesian companies, followed by information requests to another 10 Singapore-based firms with plantation or forestry interests in Indonesia.

It was the first time the agency had issued such information notices to Singapore-registered companies under the Transboundary Haze Pollution Act since the law came into effect in 2014.

Singapore has also assembled a specialist panel of legal, audit and investigative professionals to examine corporate structures, operations and supply chains. Meanwhile, the Monetary Authority of Singapore has instructed banks to assess the environmental risks of their own activities and those of their customers that could be linked to the haze, including their exposure to deforestation and pollution. The government also plans to strengthen the legal framework through amendments to the haze pollution law.

These measures mark a shift from conventional environmental diplomacy towards a more assertive model of cross-border corporate accountability. Singapore is no longer relying solely on diplomatic appeals to the country where fires originate. Instead, it is mobilising the regulatory, legal and financial instruments in its own jurisdiction to investigate companies whose activities abroad may affect its population.

The scale of Indonesia’s fire problem makes the urgency clear. MapBiomas Indonesia recorded 637,011 hectares of burned land between January and August. About 331,246 hectares, or 52 per cent, were within forest areas. These figures do not establish that every burned area contributed to Singapore’s haze, let alone identify corporate responsibility. Nevertheless, they demonstrate the scale of the environmental challenge that regional institutions have struggled to contain.

Indonesia has legitimate authority over its territory, natural resources and law enforcement, and Singapore has a legitimate interest in protecting its population from pollution originating beyond its borders. Neither interest automatically cancels the other.

The 1992 Rio Declaration’s no-harm principle recognises that states have a responsibility to ensure that activities within their jurisdiction or control do not cause significant environmental damage to other states. This does not impose automatic liability for every fire or pollution incident. Rather, it requires appropriate preventive measures, monitoring and due diligence.

Singapore’s Transboundary Haze Pollution Act tests how far domestic legislation can reach when environmental harm crosses national boundaries. The law allows action against companies that cause or contribute to haze pollution in Singapore, even when relevant activities occur overseas.

However, Singapore cannot conduct searches, compel witnesses to appear in court or seize evidence in Indonesia without regard to Indonesian law and the applicable procedures for cross-border cooperation. Proving causation also remains difficult.

This is where Asean’s institutional limitations become apparent. The Asean Agreement on Transboundary Haze Pollution, signed in 2002, provides a framework for prevention, monitoring, information exchange and mutual assistance.

Yet it does not establish a powerful regional enforcement authority capable of prosecuting corporations across national jurisdictions. Asean’s preference for consensus, non-interference and state-led cooperation has helped preserve political cohesion, but also constrained collective responses to problems that demand stronger accountability.

The region has integrated its markets more effectively than it has integrated the institutions needed to govern cross-border consequences. Corporate accountability is consequently becoming a new arena of regional power. Singapore’s approach reaches beyond plantation operators to corporate affiliations, ownership structures and financing relationships.

Its central bank’s intervention is particularly significant as banks may review financing conditions, restrict exposures or reconsider relationships where clear environmental breaches are established. This creates economic pressure beyond the courtroom, although an investigation or regulatory notice shouldn’t be mistaken for a finding of guilt.

Indonesia and Singapore have recognised that unilateral action alone cannot resolve the problem. On October 27, their foreign ministers announced plans for a joint task force to coordinate investigations and exchange information on companies linked to forest and land fires.

The proposed cooperation includes cross-border evidence gathering and financial intelligence. This offers a practical route to reconciling enforcement with territorial sovereignty.

The Association of Southeast Asian Nations should build on this opening. A regional environmental accountability framework could establish common procedures for sharing satellite data, concession records, beneficial ownership information and corporate evidence.

It could also facilitate joint investigations and mutual legal assistance, while ensuring that enforcement within each country’s territory remains subject to its domestic laws. Such arrangements would strengthen accountability without creating an unrestricted licence for unilateral intervention.

The challenge is not to weaken sovereignty but make it more responsive to an interconnected region. Asean must move beyond declarations of cooperation towards institutions capable of delivering results.