Congress shall have no power to pass any retroactive Bill unless approved by a two-thirds vote of both Houses except Congress shall never impose taxes retroactively.
Congress shall pass no retroactive Bills, civil or criminal, without a two-thirds vote and without an express statement that retroactivity is in the public interest, does not take or impair vested rights, and does not create new obligations or impose new duties prior to the effective date of the Bill, except Congress shall never impose any tax retroactively.
The notion that a law could somehow apply retroactively has been universally condemned and is currently covered by Article I, § 10 of the Constitution (“No Bill of Attainder or ex post facto law shall be passed.”). States are prohibited from passing an “ex post facto law, or law impairing the obligation of Contracts …”. James Madison argued that retroactive legislation offered special opportunities for the powerful to obtain special and improper benefits. However, the Supreme Court has interpreted these constitutional provisions to apply only to penal litigation.
In Landgraf v. USI Film Products, 511 U.S. 244 (1994), the Supreme Court cited an earlier case that “Congressional enactments and administrative rules will not be considered to have retroactive effect unless their language requires this result.” The court said the Constitution only prohibited penal retroactivity and therefore permitted other types of retroactivity when congressional intent was clear.
Although it may be appropriate in some cases to have retroactive laws (emergencies or to correct clear mistakes), they should certainly not be passed unless a super majority of Congress expressly recognizes why they are important. For this reason a two thirds vote has been specified as required to achieve the level of unanimity required to meet the expectations of governmental fair dealing with the public.
With respect to taxation, Congress has taken the position that once a Bill has been filed and the content of the law becomes known, it is fair to pass the law at a later date but make it effective at an earlier date. Most people disapprove of this practice.
Every day people make decisions and take actions according to the law as it then exists. The idea that Congress can somehow change the mix of facts with a retroactive law and thereby impose a greater burden on the decision maker than existed at the time of the decision is morally wrong. Some persons will take the risk. Other persons will do nothing until the matter is settled in Congress. This delay interdicts economic growth in numerous and unforeseeable ways not predictable by anyone, including Congress.
If Congress wants to raise taxes, it should get about it quickly and efficiently. It should not pull the rug out from underneath the people who make decisions on existing law before a new law is passed.