Border Tunnel Prevention Act of 2006 (HR 4830)
This bill sets explicit sentencing for tunnels built between the United States and another country. This includes those who allow the tunnels to be built on their land.
Sentencing is no less than 20 years for the builders of the tunnel and 10 years for the land owners who allow it or finance it. The sentencing is doubled for smugglers of illegal aliens, goods, controlled substances, weapons of mass destruction or a member of a terrorist organization.
Full text of the bill.
If you can believe it, we currently have no laws on the books addressing this. I'll be watching to see what Congress members could possibly vote against this bill.
Update: This bill has passed the House