To the Senate of the United States:
The act of Congress "to appoint a day for the annual meeting of Congress," which originated in the Senate, has not received my signature. The power of Congress to fix by law a day for the regular annual meeting of Congress is undoubted, but the concluding part of this act, which is intended to fix the adjournment of every succeeding Congress to the second Monday in May after the commencement of the first session, does not appear to me in accordance with the provisions of the Constitution of the United States.
The Constitution provides, Article I, section 5, that--
Neither House, during the session of Congress, shall, without the consent of the other, adjourn for more than three days, nor to any other place than that in which the two Houses shall be sitting.
Article I, section 7, that--
Every order, resolution, or vote to which the concurrence of the Senate and House of Representatives may be necessary (except on a question of adjournment) shall be presented to the President of the United States, and before the same shall take effect shall be approved by him. * * *
Article II, section 3, that--
He (the President) may, on extraordinary occasions, convene both Houses, or either of them, and in case of disagreement between them with respect to the time of adjournment he may adjourn them to such time as he shall think proper. * * *
According to these provisions the day of the adjournment of Congress is not the subject of legislative enactment. Except in the event of disagreement between the Senate and House of Representatives, the President has no right to meddle with the question, and in that event his power is exclusive, but confined to fixing the adjournment of the Congress whose branches have disagreed. The question of adjournment is obviously to be decided by each Congress for itself, by the separate action of each House for the time being, and is one of those subjects upon which the framers of that instrument did not intend one Congress should act, with or without the Executive aid, for its successors. As a substitute for the present rule, which requires the two Houses by consent to fix the day of adjournment, and in the event of disagreement the President to decide, it is proposed to fix a day by law to be binding in all future time unless changed by consent of both Houses of Congress, and to take away the contingent power of the Executive which in anticipated cases of disagreement is vested in him. This substitute is to apply, not to the present Congress and Executive, but to our successors. Considering, therefore, that this subject exclusively belongs to the two Houses of Congress whose day of adjournment is to be fixed, and that each has at that time the right to maintain and insist upon its own opinion, and to require the President to decide in the event of disagreement with the other, I am constrained to deny my sanction to the act herewith respectfully returned to the Senate. I do so with greater reluctance as, apart from this constitutional difficulty, the other provisions of it do not appear to me objectionable.
Andrew Jackson, Veto Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/201713