QDROphile is right that a nonqualified deferred compensation plan is not governed by or subject to the same ERISA and Internal Revenue Code rules and conditions that usually apply to an IRC § 401-qualified plan.
But if the deferred compensation is provided by a plan established or maintained by an employer (and is not a governmental plan or a church plan), the plan might be governed by title I of the Employee Retirement Income Security Act of 1974. If so, the exceptions that ERISA sections 201, 301, and 401 provide for an unfunded select-group plan excuse such a plan only from Parts 2, 3, and 4 of subtitle B of title I of ERISA, and do not excuse a plan from Parts 1 and 5.
Alternatively, an agreement with an employee – especially if just one has deferred compensation – could be so lacking in a need for administration that it might not be a plan (within the meaning of ERISA § 3(2)(A)).
Whether ERISA or State law governs, a deferred compensation agreement might include an implied obligation of good faith and fair dealing. So Lou S.’s suggestion about getting a lawyer’s advice makes sense not only to get a clear picture of the employer’s rights and remedies but also because in a later dispute the employer might be well served by showing it acted in good faith and with fair dealing by seeking and following a lawyer’s advice.