Sen. Sheldon Whitehouse (D-R.I.) on Monday urged Chief Justice John Roberts to investigate Justice Samuel Alito over his recent comments about Supreme Court ethics.

In a seven-page letter, Whitehouse lodged an ethics complaint about Alito’s recent interview with The Wall Street Journal’s opinion section, in which the conservative justice said Congress has no authority to regulate the high court.

Whitehouse, a leading critic in the Senate of ethics standards at the Supreme Court, urged Roberts to “take whatever steps are necessary” to probe the matter.

“On the Senate Judiciary Committee, we have heard in every recent confirmation hearing that it would be improper to express opinions on matters that might come before the Court. In this instance, Justice Alito expressed an opinion on a matter that could well come before the Court,” he wrote.

The letter was first reported by The Washington Post.

As Democrats renewed their push for a Supreme Court ethics bill, Alito sat down with the Journal’s conservative-leaning opinion section for a wide-ranging interview in July. He called recent stories about him “nonsense” and suggested he had to defend himself because the Supreme Court bar wasn’t doing so.

“I know this is a controversial view, but I’m willing to say it,” he told the Journal. “No provision in the Constitution gives them the authority to regulate the Supreme Court — period.”

Whitehouse took Alito’s comments as a direct response to his bill, which advanced out of the Senate Judiciary Committee this summer and would require the justices to adopt a binding code of ethics.

“Justice Alito’s decision to opine publicly on the constitutionality of that bill may well embolden legal challenges to the bill should it become law. Indeed, his comments encourage challenges to all manner of judicial ethics laws already on the books,” the senator wrote in his Monday letter.

The Hill has reached out to Alito and Roberts for comment through a court spokesperson.

Whitehouse further took aim at how one of the two authors of the opinion piece was David Rivkin, an attorney who represents conservative judicial activist Leonard Leo and rebuffed Whitehouse’s demand for information from Leo in July.

Whitehouse had requested information about Leo’s involvement with a 2008 Alaskan fishing trip that Alito took, with his flight reportedly being provided by a billionaire hedge fund owner.”

The trip was reported in one of multiple stories published by ProPublica and other news outlets that have fueled Democrats’ push for stronger ethics rules. Rivkin pushed back by calling the effort one-sided and having overlooked the ethics woes of the high court’s liberal justices.

“The timing of Justice Alito’s opining suggests that he intervened to give his friend and political ally support in his effort to block congressional inquiries. It appears that Justice Alito (a) opined (b) on a specific ongoing dispute (c) at the behest of counsel in that dispute (d) to the benefit of a personal friend and ally,” Whitehouse wrote Monday, according to the letter published by The Washington Post.

The Hill has reached out to Rivkin for comment.

Updated 3:03 p.m.