Iowa Code § 453B.13: Credit for previously paid taxes.

If another state or local unit of government has previously assessed an excise tax on a taxable substance, the taxpayer shall pay the difference between the tax imposed under this chapter and the tax previously paid. If the tax previously paid to the other state or local unit of government was equal to or greater than the tax imposed under this chapter, no tax is due. The burden is on the taxpayer to show that an excise tax on the taxable substances has been paid to another state or local unit of government.