As a general matter, retroactive tax hikes are bad tax policy and even worse governance.  There's a reason the Founding Fathers put a prohibition on "ex post facto" laws in the Constitution.  When it comes to taxes, it's not fair for employers and families to comply with the tax code only to find that the rules then changed after the fact, and after it's too late to do anything about your original choice.  It's "heads I win, tails you lose" government at its worst.

Yet that is precisely what Senate Finance Committee Chairman Max Baucus (D-Mont.) is proposing to do as a way to finance the Highway Bill.

Chairman Baucus proposes the retroactive repeal of $3 billion worth of tax credits (and the ability to carry them forward) from 2009.  The retroactive repeal also affects 2010 and 2011 tax returns as well.  Capital has been allocated.  Tax accounting decisions were made.  For Congress to re-write 2009 tax law now is patently-unfair, and creates a horrible precedent for tax policy going forward.

Suppose Congress decides to repeal the mortgage interest deduction in 2009, to take an extreme example.  The 42 million American families that claimed that deduction would have to go back and pay money they probably don't have and only have to pay because Congress changed the rules years later.  Sound fair to you?  If not, it's likely because you have a basic sense of fair play.

If Congress wants to find a way to pay for the Highway Bill, there are $3.6 trillion other ways to do so.  It's called cutting spending, and it's what responsible state governments, families, and employers across America have been doing for years.  Retroactively raising taxes is not the answer.