5 CFR § 842.309 - Contract service.
Contract service with the United States will only be included in the computation of, or used to establish title to, an annuity under chapter 84 of title 5, United States Code, if—
(a) The employing agency exercised an explicit statutory authority to appoint an individual into the civil service by contract; or
(b) The head of the agency which was party to the contract, based on a timely-filed application, in accordance with section 110 of Public Law 100-238, and the regulations promulgated by OPM pursuant to that statute, certifies that the agency intended that an individual be considered as having been appointed to a position in which (s)he would have been subject to subchapter III of chapter 83 of title 5, United States Code, and deposit has been paid in accordance with OPM's regulations.