When attempting to avoid compliance with a subpoena, it is good practice to converse with the attorney responsible for issuing it to see if you can negotiate a limitation on the subpoena or be relieved of having to comply with the subpoena altogether.
Where a subpoena commands a person to produce documents for inspection or copying, that person may object to it. The objection must be in writing, and delivered to the person or attorney designated in the subpoena as being responsible for issuing it. The objection must be made within 14 days after receiving the subpoena. However, if the subpoena gives fewer than 14 days for compliance, then at any time before the time set by the subpoena for compliance. Fed. R. Civ. P. 45(c)(2)(B).
If the objection is made in writing, delivered to the appropriate person, and delivered on time, then the person on whose behalf the subpoena was issued and served has no right to inspect or copy the subpoenaed documents without a court order. Failure to follow the rules for the written objections gives the person responsible for the subpoena the right to move to compel compliance and to seek to hold the person to whom the subpoena is directed in contempt of court. Fed. R. Civ. P. 45(c)(2)(B), (e).
The safest course is to deliver a written objection in accordance with the provisions of Rule 45 even if negotiations with the person responsible for the subpoena are going well. The written objection has the legal effect of suspending the duty to comply with the subpoena until a court decides the matter.