Endorsement of medical documents, MD vs PA or NP or Nurse

I just (3 weels ago) was injured on the job, and a case was opened up as well as having a case worker assigned to me.

I have a follow up shortly, but for the initial paper work and the previous follow up, the case worker made a big deal about the paperwork being signed by an MD and not the PA who handled the injury.

The portion of the email from the caseworker stated "Please note that , per FECA guidelines, any medical paperwork related to your WC claim my include a physicians (MD or DO) signature"

I asked my provider, and his response was a NP or PA is considered competent medical authority and shouldn't be an issue.

Is the caseworker correct, and I have to force the issue of having a doctor sign or co-sign my paperwork? I havent seen my PCP in 3 years, as the office PA and NP do all my physicals and other medical appointments. I also went to the FECA website but couldnt find specifically where this is addressed.