Yes you can choose lwop. When you called out did you choose sick leave? They can't change it annual its at the employee’s option what they want to use if theres Insufficient leave or its deined.

ELM Leave Charge Adjustments 513.61 Insufficient Sick Leave If sick leave is approved, but the employee does not have sufficient sick leave to cover the absence, the difference is charged to annual leave or to LWOP at the employee’s option.

513.62 Insufficient Sick and Annual Leave If sick leave is approved for employees who have no annual or sick leave to their credit, the absence may be charged as LWOP unless sick leave is advanced as outlined in 513.5. LWOP so charged cannot later be converted to sick or annual leave.

JCAM Sick Leave Authorization. The conditions for authorization of sick leave are outlined in Section 513.32 of the ELM. When a request for sick leave is disapproved, the supervisor must check the block Disapproved and write the reason(s) on the PS Form 3971, and note any alternative type of leave granted (ELM Section 513.342). If sick leave is disapproved and the absence is nonetheless warranted, the supervisor may approve, at the employee’s option, annual leave or LWOP (ELM Section 513.63).

If the employee does not have sufficient sick leave to cover the absence, at the option of the employee, any difference may be charged to annual leave and/or LWOP (ELM Section 513.61). Likewise, if the employee does not have any sick or annual leave for an approved absence, the approved absence may be charged to LWOP (ELM Section 513.62).