Supreme Court rulings it seems. This is the law: https://www.law.cornell.edu/uscode/text/8/1357# https://www.law.cornell.edu/uscode/text/8/1357# But it only sa

Supreme Court rulings it seems. This is the law: https://www.law.cornell.edu/uscode/text/8/1357# https://www.law.cornell.edu/uscode/text/8/1357# But it only says "any reasonable distance". SCOTUS appears to have come up with the 100 mile limit in various cases over time.