No. The government can levy custom duty whenever it pleases. Custom duties are levied by the government in order to increase the country’s revenue, as well as to provide protection to domestic industries from competition from other countries. While the government does announce custom duties during the Budget presentation, that’s not the only time it levies these duties. This is because these duties are also aimed at balancing the imbalance caused by raw material or product prices domestically as well as abroad. Thus, whenever the government feels that any particular industry is suffering due to demand supply mismatch, it tries to intervene by making the market condition favourable for them. Custom duties are levied to rectify demand supply mismatch on import as well as export fronts.