Burrowing Under Border: Not Illegal?
Josh at South Park Pundit has a post about it not being illegal to tunnel under the border into the United States.
Entering the US without going through customs is still illegal, but building the tunnel itself is not.
However, I'll bet it's illegal, at least the way they usually do it, if you apply the right laws!
In Washington State if you move more than a small amount of dirt you need an excavation permit, a site plan, and a signed off site review. If you are making modifications to the basement of your house for the tunnel, you need a building permit and final inspection.
You also need to document that it's not a wetland. Probably not a problem on the Mexican border, but you'd be surprised what is now considered to be wetlands!
The tunnel building could certainly be determined to be a construction site, requiring OSHA compliance once into the US. In some states it might even require union representation and collective bargaining for the workers/miners. It certainly also qualifies as mining, and there are probably a whole book of laws and regulations on that.
A full Endangered Species Act Assessment may also need to be done to make sure no critical habitat for an endangered species is lost.
Not to mention environmental impact statements and assessments, shoreline management planning, and more.
If the tunnel has lights, it may need to be up to code electrically, and require an electrical permit and inspection before use.
There may not be a state "Anti-Tunneling" law, but a good prosecuting attorney could keep them locked up for other permit violations for the rest of their lives!
Believe it or not, a few years ago I built a small barn on my farm, and the final approval required a notarized form stating that I was aware that my barn was being built within 400 yards of agricultural activity!