READ: The rare filing that underscored the stakes in the Supreme Court's Lisa Cook ruling

The case drew an extraordinary amicus brief from leading figures in American economic policy, who urged the court to preserve the Federal Reserve's independence and warned that expanding presidential control over the central bank could undermine confidence in U.S. monetary policy.

An amicus brief is a filing by a non-party that offers information, expertise or legal arguments to help a court decide a case.

The group, which also includes seven former White House economic advisors, spans roughly five decades of U.S. economic policymaking.

Such intervention is rare, as former Fed chairs and Treasury secretaries typically steer clear of public legal battles.

In the 32-page amicus brief, the group argues that allowing the Trump administration to remove a sitting Fed governor would "erode public confidence in the Fed's independence and threaten the long-term stability of the economy."

That concern, the group argues, is already playing out in real time.

"Sectors that pay close attention to the Federal Reserve - including the financial markets, the public, employers and lenders - are watching the current dispute over the President's removal of Governor Cook to judge how credible the Fed will be going forward."

Solicitor General D. John Sauer said Cook's amici filing did not address the "legal issues at the heart of this case."

The case has emerged as a major test of the legal protections that have long insulated the Federal Reserve from direct political control.