19 U.S.C. § 535

In all suits and proceedings other than criminal arising under any of the revenue laws of the United States, the attorney representing the Government, whenever, in his belief, any business book, invoice, or paper, belonging to or under the control of the defendant or claimant, will tend to prove any allegation made by the United States, may make a written motion, particularly describing such book, invoice, or paper, and setting forth the allegation which he expects to prove; and thereupon the court in which suit or proceeding is pending may, at its discretion, issue a notice to the defendant or claimant to produce such book, invoice, or paper in court, at a day and hour to be specified in said notice, which, together with a copy of said motion, shall be served formally on the defendant or claimant by the United States marshal by delivering to him a certified copy thereof, or otherwise serving the same as original notices of suit in the same court are served; and if the defendant or claimant shall fail or refuse to produce such book, invoice, or paper in obedience to such notice, the allegations stated in the said motion shall be taken as confessed unless his failure or refusal to produce the same shall be explained to the satisfaction of the court. And if produced, the said attorney shall be permitted, under the direction of the court, to make examination (at which examination the defendant or claimant, or his agent, may be present) of such entries in said book, invoice, or paper as relate to or tend to prove the allegation aforesaid, and may offer the same in evidence on behalf of the United States. But the owner of said books and papers, his agent or attorney, shall have, subject to the order of the court, the custody of them, except pending their examination in court as aforesaid.