SAN FRANCISCO — In case there was any question whether large law firms would balk at a clash with President Donald Trump, even Jones Day, a firm that has seen at least a dozen of its lawyers take key posts in the Trump administration, joined the legal fight Monday against the president’s executive order limiting entry to the U.S. for citizens of seven predominately Muslim countries.

In an amicus brief filed with the U.S. Court of Appeals for the Ninth Circuit on behalf of four constitutional scholars, Jones Day lawyers challenged the administration’s position that the executive branch has “unreviewable authority to suspend the admission of any class of aliens.”

The move spurred acting Solicitor General Noel Francisco and acting assistant attorney general Chad Readler, both former Jones Day lawyers, to hold back from signing the Justice Department’s latest brief Monday afternoon.

“The acting solicitor general and acting assistant attorney general have refrained from signing this brief, out of an abundance of caution, in light of a last-minute filing of an amicus brief by their former law firm,” the brief stated.

That surprise abstention of two of the Justice Department’s highest-ranking Trump appointees was just one sign of how frenetic the legal maneuvering has been since U.S. District Judge James Robart in Seattle entered an order Feb. 3 temporarily blocking Trump’s travel ban and forcing the government to allow individuals from the seven nations with valid travel documents into the United States.

A whirlwind of briefing began the morning of Feb. 4, and several major law firms, including Hogan Lovells, Arnold & Porter Kaye Scholer, Mayer Brown, and Akin Gump Strauss Hauer & Feld have not shied away from rumbling with the Trump administration.

All the Big Law briefs back the states of Washington and Minnesota in their bid to uphold Robart’s ruling. The amicus campaign comes as some large-firm lawyers have organized to raise funds and recruit lawyers to represent those targeted for removal and puts the firms in alignment with at least some corporate clients; nearly 100 companies represented by Mayer Brown signed an amicus brief opposing the travel ban.

In the Ninth Circuit case, a Jones Day team led by New York appellate specialist Meir Feder weigh in on behalf of professors from Boston University, Yale Law School, University of Texas School of Law, and New York University School of Law.

“In this case, the unusual selection of seven countries whose nationals are precluded from using the valid visas that they have or from obtaining visas for a period of time, coupled with the apparently extensive evidence that the seven countries were selected because of the religion of their citizens, raises a host of constitutional questions as to the rationality of the executive order and as to its discriminatory impact,” Feder wrote.

When contacted by email Monday, Feder wrote that the firm would “let the brief speak for itself.”

In the underlying case, Ninth Circuit Judges William Canby Jr. and Michelle Friedland on Feb. 4 denied an emergency government request to overturn Robart’s injunction barring enforcement of the order. Circuit Judge Richard Clifton will join Canby and Friedland in further reviewing Robart’s ruling. Telephonic argument has been set for 3 p.m. Tuesday, and a decision is expected from the panel this week.

Lawyers who have joined in the amicus campaign said Monday that they welcomed the opportunity to work on a constitutional case of national significance.

Hogan Lovells partner Neal Katyal, who represents the state of Hawaii alongside lawyers from the state’s attorney general’s office, filed a motion to intervene in the Ninth Circuit case. Katyal said in an email he has been in around-the-clock meetings dealing with the state’s challenge to the executive order. “I’m lucky to be at a law firm that sees this kind of work as part of its core mission—and to have as a long-standing client the state of Hawaii, which shares in that mission,” said Katyal, the former acting U.S. solicitor general in the Obama administration.

Plaintiffs firm Hagens Berman Sobol Shapiro filed a brief on behalf the Service Employees International Union at both the district court and the Ninth Circuit. Partner Steve Berman said about a dozen lawyers at the firm volunteered after the union approached the firm last week.

“Personally I think that most people in my firm think the presidential order has crossed the line and if we can help in that fight let’s do it,” Berman said. Berman said that Trump’s Twitter message referring to Robart as a “so-called judge” has only strengthened his feelings on the matter, since he knows the judge from his days in private practice in Seattle. “Defending [Robart's] order brings me a lot of pleasure,” Berman said.

Also on Monday, the attorneys general of 15 states and the District of Columbia filed a separate amicus brief of their own. In a prepared statement, California Attorney General Xavier Becerra, who joined the brief, said that the executive order “threatens to rip apart California families, risks their economic well-being and defies centuries of our American tradition.” Becerra said that the state’s universities, medical institutions, business and tax base would all be harmed if the order is allowed to stand.

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