Duty-free imports and export obligation rules govern EOUs and related parks, subject to net foreign exchange compliance. EOU/EHTP/STP/BTP units primarily export goods and services while being permitted to import or procure inputs, including capital and second hand goods, without payment of customs duty and related cesses subject to notifications, actual user conditions and statutory permissions. Units must remain positive on Net Foreign Exchange over cumulative five year blocks; issuance and validity of Letter of Permission/Intent and execution of a Legal Undertaking govern establishment, extensions and compliance. Failure to meet NFE or other conditions renders units liable to penal action and loss of benefits.