Does this qualify as insubordination?

On December 30, 2009 I was written up for insurbordination by my Supervisor.
I completely disagree with the reasons I am being written up for
insubordination. I did not, not accept the initial request to deliver the packages to the Post Office, I had been doing it from August 2009.
I did want to anymore do to these circumstances.
On Dec. 09, 2009 an email went out from the shipping dept. telling us to ship Class 2 controlled subsyances via USPS, due to the fact that FedEx was losing packages. I told my supervisor that I felt uncomfortable being the one responsible for taking the CII's to the Post Office because of the poor process that is place to protect the employee from liability and risk. Could the postman begin picking them up here at the pharmacy. Was told our volume was not high enough.
I was told by my Supervisor that I had to continue
delivering pkgs containing Class II controlled substances to the Post Office.
On Dec. 29, 2009 a pkg containing a CII went missing, I was given an order from my supervisor to try and track it down because it was looking like it might not have made it to the post office, I was not able to find it, but while trying I learned that there is no confirmation given at the local poste office that would confirm that I had dropped them off, And asked again if company would condsider the alternative and have the postman pick them up.
I was told No, as of now the process will continue I was to continue taking the pkgs. to the Post Office.
Again I explained that I felt uncomfortable with the process and would not be bringing the pkgs. anymore. He said that if I did not continue to deliver, I was facing termination.
I was witten up for insubordination and will again if my co-worker who is now taking them to the Post Office is out sick or off a day.
Does this qualify as insubordination?
Thank you for your time.