"The allotment system was created to help deployed service members send money home to their families and pay their creditors at a time when automatic bank payments and electronic transfers were not yet common bank services," the CFPB said in a release. "Creditors, such as auto lenders, installment lenders and retail merchants, have in recent years been known to direct service members to use the system to collect payments straight from service member earnings."

The CFPB claimed that between 2010 and 2014, the company consistently charged recurring, hidden fees against these residual balances. Fees that were not disclosed include a $5 fee to send a letter to the service member about their residual balance, a $5 fee to send a similar letter to the service member's current or past creditor and a repeat fee of $12 to $20 if the account sat idle with a positive balance for more than six months.

The CFPB alleged that MAC failed to notify service members that it charged them residual balance fees. The CFPB also said online account information did not include the fees and monthly statements were not sent to service members.

"Tens of thousands of service members had their money slowly drained from their accounts because they were not notified about the charges," the CFPB alleged. "And, since active allotments would replenish the money in the payment account, MAC continued to take such fees in a way that service members could not easily track.