The first thing you should do is find out exactly what you previously agreed to do. Do you have a copy of the rules and regulations of the Tuition Reimbursement Program? What does it state with regard to this issue?

If you previously agreed to sign such a form and to choose one of their repayment programs, then you are obligated to do just that.

If the rules and regulations are silent on the issue and you did not previously agree to do those things, then you are not obligated to sign anything, nor are you obligated to choose one of their repayment programs.

However, if the latter is true, bear in mind that legally speaking, you probably owe 100% of the money immediately. If the company offers you a repayment plan under those circumstances, they are doing you a favor.

In either case, I would do as Grace suggested: Contact your former employer, explain that you want to repay the money, that you cannot afford to do so under the terms that they sent you, and that you'd like to work out a different payment plan. If you get on a reasonable monthly payment schedule of some kind, there is really nothing more to be gained by suing you. Even with a judgment against you, the best your former employer could hope for are reasonable monthly payments. However, they may require you to sign a contract of some sort, and pay interest.