Ind. Code § 12-16.5-3-6

Sec. 6. The member states may, by unanimous agreement, amend the compact without the prior consent or approval of the federal United States Congress, to the extent the amendment is allowed under the Constitution of the United States and the constitutions of the member states. Any amendment shall be effective unless, not later than one (1) year from the approval of the amendment, the federal United States Congress disapproves of the amendment.