BISMARCK, N.D. (AP) — A federal judge has struck down North Dakota’s law targeting the practice of disguising caller ID numbers.

U.S. District Judge Daniel Traynor says the so-called anti-spoofing law is unconstitutional because it intrudes on interstate commerce regulation, a power reserved for Congress. The state Legislature passed the law last year because of complaints about harassing and scam phone calls.

Traynor ruled that because of cell phones and technology such as call-forwarding, the law has the practical effect of regulating interstate commerce because it’s impossible to determine whether the person receiving the call is physically in North Dakota.