who has the power to establish post offices
Postal Clause Article I, Section 8, Clause 7 of the United States Constitution, known as the Postal Clause or the Postal Power, empowers Congress "To establish Post Offices and post Roads".[1]
Powers of the United States Congress Congress also has the power to establish post offices and post roads, issue patents and copyrights, fix standards of weights and measures, establish courts inferior to the Supreme Court, and "To make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States, or in any department or officer thereof." Article Four gives Congress the power to admit new states into the Union.