This is a cross post from the SA (Spokane Airsoft) forums, which was cross posted from the Arnies Airsoft site. Here are the links to both:
http://arniesairsoft.co.uk/news2/14882
http://www.spokaneairsoft.com/index.php?option=com_kunena&Itemid=2&func=view&catid=28&id=4194#4223
In essence, the BATFE (former ATF) tested a JG GBB M4 that was sent in to them, modified the lower heavily, attached it to a real steel upper, and fired 3 rounds of .223 ammunition through it. Because they were able to do this (after essentially compromising the structural integrity of the lower by working on it with a dremel), the Bureau has labeled these replicas as "firearms." I still question the validity of these tests, but that's where it stands right now.
This means that, unless a lawsuit goes up against them over it, it is likely that a number of importers and retailers could be having a good portion of product confiscated, as well as fines and potential legal consequences for, essentially, gun running. Assuming they make a move beyond this, of course.
Because in Soviet Amerika, the government is always watching. For our own good, of course.