If a State fails to certify as required by this regulation or if the Secretary of Transportation determines that a State is not adequately obtaining proof-of-payment of the heavy vehicle use tax as a condition of registration notwithstanding the State's certification, Federal-aid highway funds apportioned to the State under 23 U.S.C. 104(b)(1) for the next fiscal year shall be reduced in an amount up to 8 percent as determined by the Secretary.