The Constitution of the State of Hawaii Article VII, § 2

In enacting any law imposing a tax on or measured by income, the legislature may define income by reference to provisions of the laws of the United States as they may be or become effective at any time or from time to time, whether retrospective or prospective in their operation. The legislature may provide that amendments to such laws of the United States shall become the law of the State upon their becoming the law of the United States. The legislature shall in any such law set the rate or rates of such tax. The legislature may in so defining income make exceptions, additions or modifications to any provisions of the laws of the United States so referred to and provide for retrospective exceptions or modifications to those provisions which are retrospective.