There is a doctrine called "constitutional avoidance" - if a court can decide a case on grounds without reaching a constitutional question (particularly a close question), it ought to decide the case on the alternative grounds and avoid the constitutional question.
So, for example, a court might say: This action was improper because it was not authorized by Congress. That is all we need to decide. Because we made this decision, we don't need to reach the constitutional question. Of course, if Congress had authorized this action (or now does so), and this case is back before us, we will no longer be able to take that path. We may, at that time, decide that the congressionally-authorized action is unconstitutional. But because there is no need to do reach that decision at this time, we decline to do so.
So, for example, a court might say: This action was improper because it was not authorized by Congress. That is all we need to decide. Because we made this decision, we don't need to reach the constitutional question. Of course, if Congress had authorized this action (or now does so), and this case is back before us, we will no longer be able to take that path. We may, at that time, decide that the congressionally-authorized action is unconstitutional. But because there is no need to do reach that decision at this time, we decline to do so.
Read more here: http://en.wikipedia.org/wiki/Constitutional_avoidance