law: 7. Imposition of customs duty.-
  During the period in which any duty of excise is being levied under section 6, the Central Government may, by notification, impose on all coal (including soft and hard coke), imported or brought into India from any place outside India, a duty of customs (which shall be in addition to any duty of customs for the time being leviable under any other law), at the rates equivalent to the rates of duty of excise levied under section 6.