They mentioned that in the ACLU article.
When she ordered Trump to turn over the Rudi memo by the 19th and set a date for the rest of the discovery, the judge anticipated that the defendant would object to some or all of the requests. Her written order says:
"Of course, Defendants may object to requests as allowed by the Federal Rules of Civil Procedure. To handle objections, the Court adopts the following procedure to streamline the process. If Defendants object to any discovery request, they must set forth their reasoning and legal justification, with full citations and argument, in the response to Plaintiffs. If Plaintiffs file a motion to compel regarding a specific discovery request, they must include the Defendants full objection to that request as an exhibit, which the Court will treat as the Defendants brief for deciding the motion. Defendants may not file a response brief. If the Court needs additional briefing, it will request supplemental briefing."
Arab American Civil Rights League v. Trump:
https://www.clearinghouse.net/chDocs/public/IM-MI-0004-0036.pdf (last page)
But now I wonder if this is more than an attempt to assert executive privilege broadly, or if there's something else in the memo that they prefer not to make public. Anything is possible with these lunatics.