Efficiency and predictability in the global supply chain are critical for business operations. Whether involved in manufacturing, distribution, logistics, or even in the provision of services, most business operators rely upon problem-free customs clearance in the countries in which they operate. If customs disputes do arise and are not effectively addressed, they can have a profound impact on operations, delaying delivery, creating potential civil and criminal liabilities, or even resulting in the seizure of imported goods. Often, importers or their agents can become complacent, particularly where there has been a period of months or even years of customs clearance without encountering any issues. However, disputes can arise, often relating to origin of goods, classification, and duty assessment. When not addressed early in the dispute process or through settlement, a dispute can escalate, leading to issuance of official letters of assessment by customs authorities. Once Thai customs has issued such a formal letter of assessment to an importer, discretion in settlement is gone and only the full value of the duty assessment can be accepted. At this stage, the only legal avenue for challenge is to accept the duty assessment or to litigate. This article addresses post-assessment litigation options to challenge official customs duty assessments. Customs Board of Appeals Once an official assessment is made, an importer has the right to seek a formal appeal of the customs assessment with the Customs Board of Appeals or to otherwise make payment of the full assessment within 30 days of the date it received the assessment. Extensions of time are not permitted. With few exceptions, the right to appeal does not allow the importer to defer an assessed duty payment. This means that the importer must post security for the assessed duty at the time of filing the appeal. This essentially means