Del. Const. art. VIII, § 9

Any law which shall have the effect of increasing the rates of taxation on personal income for any year or part thereof before the date of the enactment thereof, or for any year or years before the year in which the law is enacted, shall be void. 52 Del. Laws, c. 62 and 53 Del. Laws, c. 377; 84 Del. Laws, c. 281 and 85 Del. Laws, c. 5;