The PACT act (S. 1147) makes tobacco products a non-mailable material. The change in classification was an end-run in the continued battle between New York State and the Seneca Indian Reservation.
The New York State Health Department, in a 2004 study, found that 10% of New Yorkers were buying cigarettes via mail order or online and that as many as 1/3 of NY smokers were purchasing cigarettes at an Indian reservation.
According the New York State, the highest-volume online cigarette sales websites are located on the Seneca Indian Reservation.
The PACT act effectively shuts down these businesses entirely, making it a violation of federal law to mail cigarettes.