 The USPS also lacks commercial discretion and control.The U.S. Supreme Court has also upheld the USPS's statutory monopoly on access to letter boxes against a First Amendment freedom of speech challenge; it thus remains illegal in the U.S. for "anyone", other than the employees and agents of the USPS, to deliver mailpieces to letter boxes marked "U.S. Mail".The Postal Service also has a Mailers' Technical Advisory Committee and local Postal Customer Councils, which are advisory and primarily involve business customers.