Temporal limitation on commencement inserted, restricting the clause's retrospective reach with a later effective amendment date. The Expenditure-tax Act is amended by inserting the words 'but not after the 31st day of May, 2003' after 'the commencement of this Act' in section 4, clause (a), thereby imposing a cut-off on the clause's retrospective application; the amendment takes effect from the 1st day of June, 2003.