In what decision did the courts hold it illegal for federal programs to classify people by race even when the program is meant to expand opportunities for minorities?

The court case you're referring to is likely Adarand Constructors, Inc. v. Peña (1995). In this decision, the U.S. Supreme Court held that federal programs which classify individuals by race, even for the purpose of benefiting minorities, are subject to strict scrutiny under the Equal Protection Clause. The ruling emphasized that any racial classification must be narrowly tailored to serve a compelling governmental interest, thereby making it illegal to use race as a basis for federal programs without a strong justification.