Recovery of monetary penalty: demand notice requires prescribed payment by challan and submission of proof to the recovery officer. Issuance of a demand notice triggers recovery: the Secretary must serve the notice with the penalty order at the last known address, specify a minimum period for deposit, require payment by challan in favour of the designated Pay & Accounts Officer account, and mandate submission of one copy of the challan to the recovery officer for entry in the penalty recovery register; the Commission may rectify clerical or arithmetical mistakes in the demand notice.