What should I do when my state refund should be over $1,000 and instead, I received a letter discounting part of my cash donation to a 501(c)3 charity?

[SweetieJean]

Which state?  Some states have restrictions on charitable contributions.

[Carl]

There's also two basic types of charities when it comes to taxes too. You have 30% charities and 50% charities. With a 50% charity you can claim as an itemized deduction on SCH A 50% of your donations. Ditto with a 30% charity at 30% of your donated amount. Generally, a 501(c)3 is classified as either a non-profit organization or a not-for-profit organization, as opposed to a charitable organization. Donations to certain 501(c)(3) organizations, such as veterans’ organizations, nonprofit cemeteries or fraternal societies, are subject to a 30 percent limit. There are also other limits to charitable donations. LegalZoom has a pretty good "plain English" explanation at <a rel="nofollow" target="_blank" href="https://info.legalzoom.com/donations-501c3-work-taxes-23105.html">https://info.legalzoom.com/donatio...> in the section called "Limits on Deductions" that may clarify things for you.

[SweetieJean]

Actually, Federal now has 60% charities, but some states only allow 50%.  A few other states only permit deductions to in-state charities. And others have no deduction at all.
https://taxmap.irs.gov/taxmap/pubs/p526-005.htm

But TT should know all that. I suspect your state changed your income, and thus the allowable charity deduction changed as a result.