The policy.
CFR · 2024-01-01 · US · Title 5
Basic, Option A, Option B, and Option C benefits are payable according to a contract with the company or companies that issue a policy under § 8709 of title 5, United States Code. Any court action to obtain money due from this insurance policy must be taken against the company that issues the policy.
official document · source cfr-2024 · id 5:§ 870.102