And action taken against credit card companies and banks might be specially exempt from
ex post facto protection because of the adhesion contract terms (i.e., banks change the terms of their own agreement all the time)
http://en.wikipedia.org/wiki/Ex_post_facto#United_StatesHowever, not all laws with ex post facto effects have been found to be unconstitutional. One current U.S. law that has an ex post facto effect is the Adam Walsh Child Protection and Safety Act of 2006. This law, which imposes new registration requirements on convicted sex offenders, gives the United States Attorney General the authority to apply the law retroactively.<2> The U.S. Supreme Court ruled in Smith v. Doe (2003) that forcing sex offenders to register their whereabouts at regular intervals and the posting of personal information about them on the Internet does not violate the constitutional prohibition against ex post facto laws, because compulsory registration of offenders who completed their sentences before new laws requiring compliance went into effect does not constitute any kind of punishment.<3>
Another example is the so-called Domestic Violence Offender Gun Ban, where firearms prohibitions were imposed on those convicted of misdemeanor domestic violence offenses and subjects of restraining orders (which do not require a criminal conviction). These individuals can now be sentenced to up to 10 years in a federal prison for possession of a firearm, regardless of whether or not the weapon was legally possessed at the time the law was passed. Among those that it is claimed the law has affected is a father who was convicted of a misdemeanor of child abuse despite claims that he had only spanked his child, since anyone convicted of child abuse now faces a lifetime firearms prohibition. The law has been legally upheld because it is considered regulatory, not punitive—it is a status offense.
Finally, Calder v. Bull expressly stated that a law that "mollifies" a criminal act was merely retrospective and not an ex post facto law.
A large "exception" to the ex post facto prohibition can be found in administrative law, as federal agencies may apply their rules retroactively if Congress has authorized them to do so. Retroactive application is disfavored by the courts for a number of reasons,<4> but Congress may grant agencies this authority through express statutory provision. Furthermore, when an agency engages in adjudication, it may apply its own policy goals and interpretation of statutes retroactively, even if it has not formally promulgated a rule on a subject.
In the 1994 opinion United States v. Carlton, the U.S. Supreme Court unanimously held that retroactive tax laws did not violate the constitutional prohibition on ex post facto legislation, provided their retroactive application was "supported by a legitimate legislative purpose furthered by rational means".<5>