There is a nationwide shortage of organic milk. The New York Times reports it's mostly a case of a smaller supply coupled with increased demand and that the cost of organic grain and hay for feeding cows on organic farms has risen sharply, but the price farmers get for their milk has not. As a result, farmers don't feed their cows as much, leading to lower milk production.
Meanwhile, consumer demand for organic milk has risen. Major grocery chains say they've already experienced shortages -- some have already started raising prices.