The effect of the amendment was to prospectively restrict the constitutional right to citizenship by birth to those who are born on the island of Ireland to at least one parent who is (or is someone entitled to be) an Irish citizen. Those born on the island of Ireland before the coming into force of the amendment continue to have a constitutional right to citizenship. Moreover, primarily existed in legislation and it remained, after the referendum, for parliament to pass ordinary legislation that would modify it. This was done by the "Irish Nationality and Citizenship Act 2004" (the effects of which are detailed above). It remains, however, a matter for the legislature and unrestricted could be re-established by ordinary legislation without a referendum.