It depends on the wording of the contract: the law takes no position on this issue, but rather leaves it to what the parties agreed to (and obligated themselves to) in the contract. If the contract requires you pay all fees during or from the negotiation, even though incurred after you leave, you have to pay them; on the other hand, if the contract only required you to pay fees related to negotiations affecting *your job*, then once you leave (and don't have a job), you would not owe further fees. Contracts are governed by their terms or language; your obligation in this regard depends on what exactly the contract says. If you and the union disagree about this, you could refuse to pay, let them sue you (if they think it's economically worthwhile), and let a court decide what the contract says.