5 CFR § 839.1301
What if my employer determines my error is not subject to these rules?
November 4, 2020
(a) Your employer must provide you with a written decision. The decision must include the reason for the decision, and notice of your right to appeal the decision to the MSPB.
(b) If your employer determines that it cannot waive the time limit for making an election under §839.612, the decision must inform you of your right to ask OPM to review the decision. OPM will advise you in writing of your appeal rights following its review of your employer's decision.