Special deposit obligation: quarterly filers must deposit a prescribed portion of prior tax liability in early quarter months. Notification prescribes a special deposit procedure allowing certain registered persons who opt for quarterly returns to discharge tax due in the first and/or second month of a quarter by depositing in the electronic cash ledger a prescribed portion of tax liability based on the preceding quarter's return (or the last month of the immediately preceding quarter where applicable), subject to exemptions where ledger balances are adequate or liability is nil and conditional on furnishing the return for a complete prior tax period.