Laws are passed by Congress, policies are created by the executive to define things left unspecified by law, pursuant to broader powers granted by Congress.
Policies that aren't laws carry the same effective force of law, but they can be changed on a whim by the president with an executive order.
The Federal Home Loan Bank Act established the agencies that would create redlining, but the redlining itself was created by the administrators and independent agencies created by the act.
