The Wall Street Journal faced criticism on Wednesday after its highly unusual decision to let Justice Samuel A. Alito Jr. pre-empt another media organization’s article about him by publishing his response in its opinion pages.

The essay by Justice Alito in The Journal’s opinion section, which operates independently of its newsroom, ran online on Tuesday evening with the headline “Justice Samuel Alito: ProPublica Misleads Its Readers.”

An editor’s note at the top of the essay said two ProPublica reporters, Justin Elliott and Josh Kaplan, had emailed questions to Justice Alito on Friday and had asked him to respond by noon Tuesday. “Here is Justice Alito’s response,” the editor’s note said.

ProPublica published its investigation into Justice Alito several hours later on Tuesday, revealing that he took a luxury fishing trip in 2008 as the guest of Paul Singer, a billionaire Republican donor, and had not disclosed the trip nor recused himself from cases since then that involved Mr. Singer’s hedge fund.

Stephen Engelberg, the editor in chief of ProPublica, said in a statement on Wednesday that ProPublica always invited people mentioned in articles to offer a response before publication. ProPublica has run several articles in recent months about possible conflicts of interests among some Supreme Court justices.

“We were surprised to see Justice Alito’s answers appear to our questions in an opinion essay in The Wall Street Journal, but we’re happy to get a response in any form,” he said.

“We’re curious to know whether The Journal fact-checked the essay before publication,” he added. “We strongly reject the headline’s assertion that ‘ProPublica Misleads Its Readers,’ which the piece declared without anyone having read the article and without asking for our comment.”

A spokeswoman for The Journal did not immediately respond to a request for comment. In an editorial published Wednesday evening, The Journal’s editorial board wrote that it had seen ProPublica’s questions for Justice Alito and that he “clearly wanted his defense to receive public disclosure in full, not edited piecemeal.”

Bill Grueskin, a professor at Columbia University’s Graduate School of Journalism, said that while essays on opinion pages usually got some form of fact-checking, The Journal would have been unable to do so in this case because the ProPublica investigation had not yet been published.

“Justice Alito could have issued this as a statement on the SCOTUS website,” Mr. Grueskin, a former top news editor at The Journal, said in an email. “But the fact that he chose The Journal — and that the editorial page was willing to serve as his loyal factotum — says a great deal about the relationship between the two parties.”

In the article, Justice Alito argued that ProPublica’s claims that he should have recused himself from certain cases and should have disclosed certain items in a 2008 financial disclosure report were not valid.

Rod Hicks, the director of ethics and diversity for the Society of Professional Journalists, said that “it’s quite uncommon for a news outlet to allow an official to use its platform to respond to questions from a different outlet.”

“And it’s totally unheard-of to post that response before the other outlet even publishes its story,” he added. “If not ethics, professional courtesy should have restrained The Journal.”