In the 2009 Melendez-Diaz case (decided by a 5-4 majority vote), the U.S. Supreme Court decided that the Sixth Amendment's Confrontation Clause gives criminal defendants the right to cross examine lab analysts who run tests that determine such matters as the alcohol content of a driver's blood or whether white powder is an illegal drug. Outraged prosecutors in many states have attacked the practical effect of the decision. They argue that under-funded and under-staffed forensic labs were unable to keep up with the demands for testing even before Melendez-Diaz was decided, and that if analysts have to hang around courtrooms the labs will fall so far behind that cases will have to be dismissed. Prosecutors also argue that cross examination is unnecessary when analysts don't exercise subjective judgment but instead simply report the results of tests that machines carry out.
In Briscoe v. Virgina (2010) the Court passed up a chance to clarify the scope of Melendez-Diaz. Briscoe involved the legitimacy of a state law that allowed prosecutors to offer lab test reports into evidence without calling the analysts as witnesses, and then (upon request from the defendant) producing the analysts for defendants to examine as part of the defense case. The Court chose not to decide whether this procedure is constitutional, instead returning the case to the state for "consideration in the light of the decision in Melendez-Diaz." So for some time to come, the increasingly bitter confrontation over the scope of the Confrontation Clause continues.