The Thai Timber Legality Assurance System or THA-TLAS annex is the core of the FLEGT VPA. THA-TLAS is the system to verify and license legal timber products, effective for products sold domestically and exported.

The annex details the functions of the system, from compliance checking and licensing to the independent monitoring of the system; where third-partied organizations will be contracted to monitor the system’s efficiency and transparency

THA-TLAS consists of five components:

1. Legality verification
   The system will check the legal compliance of the timber products. Laws and regulations that the operators have to follow are listed in Annex 2 Thai Timber Legality Definition.
2. Supply Chain Control
   Aside from legality verification, the system will check that the supply chain of the timber products is tracked and recorded to ensure timber traceability. A process of supply chain control is described in Annex 6 Thai Supply Chain Controls.
3. Verification of Compliance
   The designated government agency will check the compliance of the timber products against the two above criteria: legality and supply chain control.
4. FLEGT Licensing
   Verified timber products will receive the FLEGT license given out by the designated government agency.
5. Independent Audit
   Thailand will contract an independent audit to assess, produce reports and provide recommendations on the THA-TLAS system. This function is in place to ensure the efficiency and transparency of the system.