WASHINGTON — Judicial independence is under grave threat on several fronts, Chief Justice John Roberts wrote on Tuesday in an unusually urgent and somber year-end report on the state of the federal judiciary.

“Violence, intimidation and defiance directed at judges because of their work undermine our Republic, and are wholly unacceptable,” he wrote.

The report, which arrived in the wake of questions about the court’s ethical standards and a drop in its approval ratings, said some criticism of judges’ work is healthy, warranted and welcome.

“Unfortunately, not all actors engage in ‘informed criticism’ or anything remotely resembling it,” he wrote. “I feel compelled to address four areas of illegitimate activity that, in my view, do threaten the independence of judges on which the rule of law depends.”

One, he wrote, was “violence directed at judges for doing their jobs.” The number of hostile threats and communication directed at judges has more than tripled in the past decade, he wrote. “In extreme cases,” he added, “judicial officers have been issued bulletproof vests for public events.”

At a judicial conference in September, Justice Amy Coney Barrett said she had been given one, prompting questions from her 13-year-old son.

Until 1979, the chief justice wrote, only one federal judicial officer had been killed, in an incident unrelated to his judicial work. There have been a half-dozen killings of judges or their relatives in response to court rulings since then, he wrote.

The chief justice also decried the release on the internet of judges’ home addresses and phone numbers, leading to “angry, profane phone calls” and “visits to the judge’s home, whether by a group of protesters or, worse, an unstable individual carrying a cache of weapons.”

After the Supreme Court in 2022 overturned Roe v. Wade, which had established a constitutional right to abortion, there were protests at the houses of justices in the majority, and an armed man was arrested near the home of Justice Brett Kavanaugh. The man, Nicholas John Roske, was charged with attempted murder and has pleaded not guilty.

Politicians bore some blame, the chief justice wrote.

“Public officials, too, regrettably have engaged in recent attempts to intimidate judges — for example, suggesting political bias in the judge’s adverse rulings without a credible basis for such allegations,” Roberts wrote, adding: “Public officials certainly have a right to criticize the work of the judiciary, but they should be mindful that intemperance in their statements when it comes to judges may prompt dangerous reactions by others.”

A third threat to judicial independence, he wrote on Tuesday, was disinformation about the work of the courts amplified by social media. Some of it, he said, was the product of “a new and growing concern from abroad.”