I haven't been following this one closely, but after skimming through the
oral arguments I'm not too worried about the outcome.
Justices Roberts, Scalia, and Kennedy (Mr. 5th Vote) seemed to be skeptical of the Government's position. I'm assuming Alito and Thomas would vote favorably as well.
On the other hand, it would be easy for Congress to change the law if they don't like how the S. Court rules in this case. Even if we "win" this battle, Congress could change the rules and take the win away.