Income Tax (Arrangements with the States) Act 1978

• State laws must meet detailed rules about who is a resident for State purposes, what base tax the State rate will follow (a fixed proportion of the average rate of basic Commonwealth tax), how trust income is treated, and how instalments and credits work (see s.7, s.10, s.11, s.15).
• A State can choose to make a payment to the Commonwealth that will be applied by the Commissioner in partial discharge of a resident taxpayer’s Commonwealth tax liability; the Commissioner must apply the payment to the individual taxpayers for whose benefit it is made (see s.203(1)).
• The Act extensively amends the Income Tax Assessment Act 1936 and related law to recognise State income tax laws for purposes of assessments, credits, provisional tax, penalties, refunds, notices of assessment and appeals, and to allow the Commissioner to treat State credits and assigned State debts as amounts he can pay or recover (see Part III amendments, notably ss.16–35, 160ap/25, 172/28, 203/32, 208a/34).
• Employers operating across jurisdictions must track which employees are treated as residents of which State for withholding purposes; the law prescribes how employers determine that from employee notices and the employer’s circumstances (see s.10(5)–(7), s.15(2)).

Official purpose-claims and a practical test against implementation trade-offs

• The Act is framed to let States integrate their personal income tax arrangements with Commonwealth systems by having the Commonwealth administer (assess, collect, apply) certain State tax items (see s.1, s.4, s.6, s.13, s.203). That is the explicit mechanism: an assignment of rights by the State to the Commonwealth (s.13) and legislative changes so the Commissioner can operate under State law (s.76).

Costs, incentives and trade-offs the text creates

• Who bears administrative cost and who is reimbursed: the State must agree to reimburse the Commonwealth for its administration costs; the amount is to be agreed between the Commonwealth Treasurer and the State Treasurer (s.7(1)(k), s.79(4)). That creates negotiation and budgeting tasks for both governments.
• Compliance burden on employers and payroll systems: employers are required to make deductions according to differing rules depending on employer residence, place of payment and location of work, and must apply employee residency notices under s.221eb of the Income Tax Assessment Act as incorporated by this Act (see s.10, s.15, s.78). That increases payroll complexity for employers operating across State borders.
• Bureaucratic discretion and coordination risk: the Treasurer decides which States are participating/supporting and may revoke declarations (s.4). The Commissioner is authorised to exercise State-law powers (s.76) and the Treasurer may direct reports from the Commissioner about how the system worked (s.77). These features centralise operational authority in the Commonwealth but depend on intergovernmental agreement and administrative coordination.
• Legal and dispute-resolution effects: the Act modifies appeal routes and limits certain double appeals or forum-shopping (see ss.12, 30, 31). It also contains a provision that prevents courts from challenging the validity of assessments or other acts carried out under State income tax laws on the ground that those State laws fail to meet the Act’s specified requirements (see s.4(8)). Those rules change litigation strategy and finality of administrative acts.
• Treatment of credits and collections: a State credit under a State income tax law becomes a debt owed by the Commissioner (s.160ap / s.25); the Commissioner may apply those credits against other Commonwealth-administered liabilities of the taxpayer (s.160ap(2)). States assign to the Commonwealth the right to receive and recover State-assessed taxes, and those assigned debts are treated as Commonwealth debts recoverable in the prescribed places (s.13, s.208a).

Concrete implementation risks the text implies

• Administrative complexity and transitional work: the Act integrates two systems of tax law and amends many existing Income Tax Assessment Act provisions (numerous amendments across Part III). That requires substantial legal and IT alignment between Commonwealth and State systems (supported by the text’s many cross-references and amendments: Parts II–III).
• Employer/employee compliance friction: employers must apply different withholding regimes depending on employee notices and multiple jurisdictional criteria (s.10, s.15, s.78). Where an employer operates across multiple jurisdictions, determining which deductions to make and where to remit them can create errors and disputes.
• Concentrated vs diffuse costs: States receive payments and transfer collection duties; the administrative costs are negotiated and paid by States (s.7(1)(k), s.79(4)), while the compliance costs fall on many employers and affected taxpayers (s.10, s.15, s.78). The Act centralises collection into a single administration but pushes operational complexity onto employers/taxpayers.

Other practical features to note (text-based)

• Audit and accountability: receipts recovered under State income tax law and payments made to States are subject to audit by the Commonwealth Auditor‑General (s.80).
• Secrecy and information sharing: the Commissioner and staff may perform duties under State income tax laws and share necessary information; the secrecy obligations in the Income Tax Assessment Act are amended to allow that use (s.19).
• Penalties and provisional tax: the Act extends existing penalty, provisional tax and additional tax rules to include taxes or tax-like amounts under State income tax laws and adjusts how provisional tax and penalties are calculated when a State payment applies (see ss.9, 56–64). This means taxpayers and advisors must account for State payments when estimating or assessing provisional liabilities.

Bottom line (mechanical effect)

• The Act creates an integrated administrative framework: it permits and requires the Commonwealth tax administration to operate under specified State income tax law provisions, collect and apply assigned State taxes and State payments, changes appeal and credit rules to accommodate that operation, and sets out how employers and taxpayers must handle withholding and provisional payments when State arrangements apply (see Divs 1–3, Part III, ss.76, 203, 208a, 160ap).