A federal appeals court on Friday ordered special counsel Robert Mueller to file a brief on how the appointment of acting Attorney General Matthew Whitaker may impact a case involving a former aide to Roger Stone who is challenging a subpoena from Mueller.

The order applies to lawyers representing Stone's former aide, Andrew Miller, who is also challenging the constitutionality of Mueller's appointment.

In the one-paragraph order, the three-judge panel from the U.S. Court of Appeals for the District of Columbia Circuit told both Mueller and lawyers for Miller that they have until Nov. 19 to turn in briefs that describe if there will be legal ramifications stemming from Whitaker’s appointment.

Whitaker took over for fired Attorney General Jeff Sessions on Wednesday, and now oversees Mueller.

Deputy Attorney General Rod Rosenstein appointed Mueller in May 2017, which the special counsel’s office has argued in various cases as a constitutional move. Rosenstein had been in charge of oversight of Mueller because of Sessions’ recusal.

Oral arguments in the case came Thursday, and the Justice Department shakeup was discussed then.

“Argue this case as if it was being argued yesterday morning,” said Judge Karen Henderson, who said the panel would hear the case as if the shakeup had not happened.

Mueller’s team subpoenaed Miller in May to testify before a grand jury. Miller immediately began fighting the subpoena.

In July, a federal judge ordered Miller appear before the grand jury, but that has been delayed since the appeal.

Stone, a Republican operative, worked on the Trump campaign as an adviser, before leaving in August 2015.

He has since been under investigation by Mueller for collaborating with WikiLeaks founder Julian Assange in 2016 in an effort to leak emails to bring down Democratic nominee Hillary Clinton.

A lawyer for Miller told reporters Thursday that if they lose at the appeals court level, they will appeal the case to the U.S. Supreme Court.

[Read more: Trump's new line of attack on Russia inquiry: 'Mueller was not Senate confirmed']