Question: If a party brings suit under federal law and it makes its way up to the Supreme Court and none of the parties specifically claim that the statute is unconstitutional but simply have a dispute over its interpretation of a clause....but in fact if you would examine the statute you would find it unconstitutional, can the Supreme Court itself raise this as an issue or will it merely rule based on the interpretation of the clause and leave the question of whether the statute as a whole is unconstitutional to another date?
Answer: Good question, albeit in a very long sentence. The short answer is that the Supreme Court (and really all federal courts) will not address a legal claim that has not been raised by the parties. For instance, suppose Mr. Lopez contested his conviction under the Gun-Free School Zone Act solely on the ground that he actually was not in a school zone (as defined in the Act) when he possessed the gun in question, a purely statutory question. This is a question of federal law, and thus within the subject matter jurisdiction of the federal courts. It could even get all the way to the Supreme Court (especially if there were some conflicting views in the lower courts on the issue). But no court hearing the claim would address whether the GFSZA was beyond Congress's enumerated powers, and thus unconstitutional, unless Lopez himself had pressed the claim. (Compare Justice Thomas's concurrence in Printz in this regard.)
The one exception to this general rule is if the constitutional question concerns the court's jurisdiction -- its power to speak. Under Article III, as we have discussed, federal courts may only decide those "cases" and "controversies" spelled out in the Constitution. This is true even if the claim that the court lacks jurisdiction is not raised by the parties. Thus, if the court believes the case presents a political question, or that the plaintiff lacks standing, it is actually required constitutionally to raise the issue sua sponte and resolve it. For if it does not, the court would effectively be issuing an advisory opinion, something that is supposed to be beyond the authority of the federal judiciary.