Home Depot is refusing to do business with the Federal Government or anyone acting as an AGENT of the Federal government when making a purchase. They'll sell to anybody including Federal Government employees and people in uniform who are not acting as an agent of the Federal Government when making their purchase.
I recall the government's position regarding a college in Arizona a couple of years ago. Even though the College officially refused to accept Federal funds to avoid being required to meet Title IX and other onerous regulatory requirements, the government took the position that since STUDENTS were personally receiving government guaranteed loans and government grants, the COLLEGE was imputed to be Federally funded and therefore subject to the regulations!!!
Home Depot does not want the government to come to court with receipts and credit card invoices totalling an amount greater than $25,000 which would then force them under the regulatory rules the government wants.