5 CFR 630.404: Requesting sick leave.

An employee must file an application—written, oral, or electronic, as required by the agency—for sick leave within such time limits as the agency may require. The employee must request advance approval for sick leave for the purpose of receiving medical, dental, or optical examination or treatment and, to the extent possible, for the purposes described in § 630.401(a)(3), (4), and (6).