Some people think it’s legal to interstate, others say it isn’t. Recently, I was told U.S. Customs says it’s legal, while the Immigration and Naturalization Service (INS) says it isn’t.
Who is in charge here?
You've hit on a vastly misunderstood point here, so let's take a moment to straighten it out.
Yes, as far as U.S. Customs in concerned, point-to-point movements within the U.S. are allowed, BUT ONLY FOR CANADIAN TRUCKS. It's not legal for the driver.
A few years ago, U.S. Customs liberalized the rules for using non-American equipment in domestic (point-to-point) movements in that country, but the INS didn’t follow.
Let's say a Canadian carrier has a terminal in the Dallas, and has American-registered trucks working from that terminal. One day, a Canadian truck comes into the terminal at the same time a hot load for Chicago shows up, but there are no more American trucks in the yard. An AMERICAN driver could get into that CANADIAN truck and make the trip, but a Canadian driver could not.
That's where the INS gets involved.
For a Canadian driver to make that move, he or she would be working in the U.S., engaged in the domestic movement of freight. The INS does not allow that.
Since the INS is a people-oriented agency, it's concerned with what people are up to. Customs is a paper-related agency so they're concerned more with violations of tax law, import duties, etc.
When INS catches a person engaged in CRIMINAL activity (Interstating), they are likely to deport the person immediately, and ask questions later.