Doesn't seem to go into effect until conditions are met in order for Connecticut not to suffer being the only state with such a requirement.http://grist.org/news/connecticut-will-label-gmos-if-you-do-too
"But the final version of the Connecticut bill includes quite a crucial catch: The labeling requirement won’t actually go into effect until similar legislation is passed by at least four other states, one of which borders Connecticut. Also, the labeling adopters must include Northeast states with an aggregate population of at least 20 million. So if, say, New York passed a labeling law, that would help a lot, as New York borders Connecticut and has a population of 19.5 million, which, combined with Connecticut’s 3.5 million, easily passes the population target.
This “trigger clause” is meant to allay fears that Connecticut could suffer negative economic impacts by going it alone — higher food prices and lawsuits from major food companies. Lawmakers are counting on safety in numbers, and hoping their state’s precedent will encourage others to follow suit."