Treasury has released an exposure draft of a tax law amendment designed to give greater certainty about the operation of debt-equity rules.The new scheme aggregation rule ensures that multiple schemes are treated as a single scheme only where this accurately reflects the economic substance of the schemes.Releasing the exposure draft yesterday, the Minister for Revenue and Financial Services Kelly O'Dwyer said the current debt and equity scheme integrity rules were "seen to be uncertain" and created difficulties.Returns on equity interests, such as dividends, may entitle a shareholder to franking credits but are not deductible to the company. Returns on debt, such as interest payments, are generally deductible to the company but do not carry franking credits.The debt-equity rules in Division 974 of the Income Tax Assessment Act are designed to ensure that interests arising from schemes are correctly classified as either debt or equity according to their economic substance.An interest that is, in substance, an equity interest cannot attract the tax treatment available to a debt interest merely because the legal form of the interest is that of a debt interest.The tax rules are designed to stop taxpayers achieving different outcomes by splitting a single scheme into multiple schemes. For example a scheme might be designed so that the return on a debt interest funds the return on equity interest in a separate scheme.Under the new rules the Commissioner of Taxation must consider whether it would be concluded that the schemes were designed to operate to produce their combined economic effect and whether the pricing, terms and conditions of the schemes are interdependent.There are carve-outs from the new rules for situations where the interdependence between schemes is only minor, such as if the test would only be satisfied because of basic funding, subordination or stapling.