Cole's letter mirrors one sent by several Republican senators, who said DOD's failure to reform its mailing system means that thousands of military voters could be disenfranchised in today's election.

Cole said the DOD's Military Postal Service Agency (MPSA) recommended that the department develop a centralized mail forwarding system for overseas addresses, but that this has not happened yet.

He said that under the current "antiquated" system, it can take two weeks or more for a redirected ballot to find its recipient. But under the new system, that would be cut to just three days.

"Implementing the MPSA recommendations is a critically important step to complete in advance of an election and a key DOD responsibility," Cole wrote. "Therefore, I encourage you to take action and modernize the mail forwarding system for redirecting blank ballots, so that our service members do not encounter the same obstacles to voting in the next election cycle."