A federal judge on Thursday ruled the firing of U.S. Federal Trade Commission member Rebecca Kelly Slaughter by President Donald Trump earlier this year was illegal.

U.S. District Judge Loren AliKhan said the Trump administration’s attempt to remove Slaughter did not comply with removal protections in federal law.

“Because those protections remain constitutional, as they have for almost a century, Ms. Slaughter’s purported removal was unlawful and without legal effect,” AliKhan wrote.

“As the Court recognised today, the law is clear, and I look forward to getting back to work,” said Slaughter in a statement. “The for-cause removal protections that apply to my colleagues and me at the FTC also protect other independent economic regulators like the SEC, the FDIC, and the Federal Reserve.”

The U.S. Justice Department late on Thursday filed an appeal of AliKhan's order to the U.S. Court of Appeals for the District of Columbia Circuit.

The dispute over Trump's firing of Alvaro Bedoya and Slaughter in March will inevitably end up before the U.S. Supreme Court, which ruled 90 years ago that FTC commissioners may be dismissed only for good cause, such as neglecting their duties. Bedoya formally resigned in June to take another job and is not part of the case.

That ruling has protected the independence of agencies that regulate road safety, stock markets, telecommunications, monetary policy and more, shielding them from direct White House control.

The Supreme Court, however, signaled it could strip that protection from agencies such as the Merit Systems Protection Board and National Labor Relations Board. Its ruling in May allowed Trump to keep two Democratic members of those boards sidelined while they challenge their terminations. The Supreme Court is led by a 6-3 conservative majority.

The White House said, "the Supreme Court has repeatedly upheld the President’s constitutional authority to fire and remove executive officers who exercise his authority. The Trump Administration will appeal this unlawful decision and looks forward to victory on this issue.” The FTC declined to comment.

AliKhan said the Trump administration wants “the FTC to be something it is not: a subservient agency subject to the whims of the President and wholly lacking in autonomy. But that is not how Congress structured it.”

The FTC, currently led by three Republicans, is structured so that no more than three of its five commissioners come from the same party.