General Discussion

As you've stated, usually FBI agents alleging a prohibited personnel practice must pursue their claims through the DOJ's internal processes, not the MSPB. A key exception exists for "preference-eligible" FBI employees, employees with "veteran's preference." These employees do have MSPB appeal rights for adverse action. Reportedly, Special Agent Giardina is a Marine combat veteran.

'Appeal Rights for FBI Employees'

"All FBI employees are covered by the normal federal-sector EEO complaints process. However, only preference eligible FBI employees may have MSPB appeal rights over adverse actions; non-preference eligible FBI employees are excluded from MSPB jurisdiction for adverse actions."

"The category of ‘preference eligible’ employees generally includes Veterans...The statute requires Veterans to have served on active duty during the Korean War, Vietnam War, Gulf War, or active duty following 9/11."

"Members of the Senior Executive Service (SES) are generally not considered preference eligible. Even those FBI employees without MSPB adverse action appeal rights are entitled to a degree of due process for may forms of adverse actions, derived from FBI internal regulations."

I don't know whether Giardina is considered a "member of the Senior Executive Service."

https://www.gelawyer.com/blog/2025/02/appeal-rights-for-fbi-employees/