Funding Conditions: Constitutional Limits on Congress's Spending Power [July 1, 2021] [open pdf - 1MB]
From the Summary: "The Spending Clause of the U.S. Constitution (Article I, Section 8, Clause 1) gives Congress broad power to authorize spending for the 'general Welfare.' The Necessary and Proper Clause (Article I, Section 8, Clause 18) supplements Congress's spending authority, allowing Congress to restrict how federal funds are used. Congress can also place requirements on the recipients of federal funds to regulate their conduct in exchange for federal funding. While funding conditions such as these are common, they are subject to constitutional limitations."
CRS Report for Congress, R46827
Congressional Research Service: https://crsreports.congress.gov/