It's by and large a cooperative process between your lawyers and the opposing party's lawyers, but its not really voluntary. If you refuse to answer a discovery request, opposing counsel can go to the judge and get a subpoena compelling you to hand the documents over. Hanging over the whole process is the threat of sanctions: for your attorneys as well as for the company. For your attorney, it is a violation of the civil rules of procedure to unreasonably refuse production requests, and it is a violation of the ethical rules to not hand over documents that are relevant and not privileged just because they might hurt your case. The former can result in sanctions, and the latter in disbarment (i.e. the professional death penalty), so while your lawyer loves you and is on your side, he will cough up the documents the other side requests. If the client refused to cooperate, the court can hold him in contempt as well.