This DC CIrcuit Court opinion cited by the 2nd Federal Judge who paused Trump’s freeze on spending:
Like the Commission here, a President sometimes has policy reasons (as
distinct from constitutional reasons, cf. infra note 3) for wanting to
spend less than the full amount appropriated by Congress for a
particular project or program. But in those circumstances, even the
President does not have unilateral authority to refuse to spend the
funds. Instead, the President must propose the rescission of funds, and
Congress then may decide whether to approve a rescission bill. See 2
U.S.C. § 683; see also Train v. City of New York, 420 U.S. 35, 95 S. Ct.
839, 43 L. Ed. 2d 1 (1975); Memorandum from William H. Rehnquist,
Assistant Attorney General, Office of Legal Counsel, to Edward L.
Morgan, Deputy Counsel to the President (Dec. 1, 1969), reprinted in
Executive Impoundment of Appropriated Fun ds: Hearings Before the
Subcomm. on Separation of Powers of the S. Comm. on the Judiciary,
92d Cong. 279, 282 (1971) (“With respect to the suggestion that the
President has a constitutional power to decline to spend appropriated
funds, we must conclude that existence of such a broad power is
supported by neither reason nor precedent.”)
In re Aiken Cnty., 725 F.3d 255, 261, n.1 (D.C. Cir. 2013).
https://storage.courtlistener.com/recap/gov.uscourts.rid.58912/gov.uscourts.rid.58912.50.0_2.pdf