Nixon's impoundment fights (1972-1975)
President Richard Nixon refused to spend billions in funds Congress had appropriated for housing, environmental, and other programs he opposed. He argued the president had inherent authority to withhold spending. The Supreme Court ruled against the administration in Train v. City of New York (1975).
The Court held that the EPA administrator couldn't withhold funds Congress had appropriated under the Federal Water Pollution Control Act.
Congress passed the Impoundment Control Act of 1974, requiring presidents to get congressional approval to cancel appropriations. The principle that the executive can't unilaterally refuse to spend appropriated funds has held since.
Solar for All tests the same boundary: whether an agency can cancel grants Congress has already obligated, when Congress rescinded only unspent balances.