If either the FTC or the Antitrust Division has reason to believe the merger will impede competition in a relevant market, they may request more information by way of "Request for Additional Information and Documentary Materials", more commonly referred to as a "Second Request".
Substance of request
A typical second request asks to gather information about the sales, facilities, assets, and structure of the businesses which are party to the transaction. This frequently requires a large number of documents to be produced, and law firms representing parties to a transaction in which a second request has been issued often must hire contract attorneys to review all the documents involved.
Parties to a transaction who feel that the second request is unnecessary or needlessly duplicative of information discovered earlier may appeal to either the FTC or the Antitrust Division (whichever agency issued the request).