I'm also an attorney (not yours - insert standard disclaimer).
Maybe I am misreading or misunderstanding, but it sounds like they have already paid and are seeking reimbursement from you based on what is an arguable interpretation of the contract provision, given advance termination within the time period that you were committing to stay.
That means that they have to seek the payment from you. If they don't like it, then they are the ones who have to pursue it from YOU & use legal means (including suit to recover) by convincing someone else that their interpretation is correct.
This is not the same as when someone provides you services and then bills you. They don't get to "bill you" and decide that you owe the money here. That's the matter of the legal dispute over the contract.
I don't know that you need to lawyer up right now, but I would make it clear in documented writing that you do not owe this money and do not intend to pay it. Then it's up to them to decide what to do about it. The worst thing that happens is they sue you, you decide it's not worth fighting about or getting a lawyer (if needed) and then you pay. Why start with the worst case scenario now?
:) Thanks for the feedback. Yes you are correct - the company approved the tuition reimbursement in July I believe and then paid me out back in August. They are now seeking reimbursement/remittance of that payment based on the fact that I "voluntarily left" the company on December 30th 2015. I left because another job opportunity came up but I would not have gone "job shopping" if they hadn't notified me of the voluntary termination.
And yes, they have not "billed" me per se but have only written a letter which states the following
"You have voluntarily resigned from your position effective December 30, 2015. Under your January 30, 2012 Key Employee Agreement (enclosed) you are obligated to reimburse the company for the following expenses: ....."
*details and description of expenses*
"Please remit a check payable to XXX Corporation... referencing blah blah blah in the amount of XXXXX"
"If XXX has not received reimbursement by February 10, 2016, this matter will be referred to our Credit & Collections Department for further follow up. You will be responsible for reimbursing XXX for any legal fees incurred by the company in connection with this matter."
The last part bothers me - it sounds like if they sue me or proceed further and incur legal costs, that I'll also be responsible for those. Is it a bridge worth crossing?
FYI, the Key Employee Agreement states the following regarding tuition:
"You agree that tuition costs for which the Company has reimbursed you and tuition advancedments which may have already been paid to you will be recovered in full if you voluntarily terminate employment within one year of completion of the respective course(s)"