It gets a little tricky here because in the US (and Canada) ex post facto laws are only forbidden in criminal matters. Laws may be applied retroactively in civi

It gets a little tricky here because in the US (and Canada) ex post facto laws are only forbidden in criminal matters. Laws may be applied retroactively in civil matters (Calder v. Bull). Further, at least in Canada, parliament can institute ex post facto laws by invoking the nothwithstanding clause. Always a little hairy politically, but legal and compatible with the rule of law. [edit] I would further argue that ex post facto laws in general are immoral.