Thanks to Jim Knecht for passing this along for everyone's knowledge. Contributions and thanks to Rich Miller and Kirston Koths of Grizzly Peak Fly Fishers.

Almost all of us fish with nymphs at least some of the time, and we often clamp split shot on to help sink the flies. Depending upon the jurisdiction, the fine is about $50 for a first offense, and loss of gear and license or even jail time is possible for repeat offenders. Many of us are unwittingly in violation because we don't know the rules, which were designed to prevent fish snagging.

View the attached files for legal and illegal diagrams.

Section 2.10(b)4 of the Freshwater Fishing Regulations reads "It is unlawful to use any weight directly attached below a hook". The rig in Fig. 2A is clearly ok since the weight is above all the flies. The key to understanding the legality of the other two rigs is the phrase "directly attached below a hook" in the text of the regulation, which the wardens take to mean "on the same line".

Thus, for Fig. 2B, the weight is above the bottom fly which makes that part ok, and the top fly is on a separate "dropper" line, which puts the weight indirectly below it, so it is also ok.  In Fig. 2C, both flies being on droppers makes the weight indirectly below each.  Seems like the safe bet is to use droppers on your multi-fly rigs.