Well yeah, but there’s nothing in the constitution that prohibited states leaving the union either. You see how that went.
Well it could be argued otherwise, iffy but
Article IV
Section 3
New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.