ABC Primetime Live did it in 1992 when reporters posed as supermarket workers at Food Lion to expose some of the chain’s practices, including the repackaging of older meat with a new sell-by date.

And now, Mother Jones magazine has published its 35,000-word investigation of a Louisiana for-profit prison, based on reporter Shane Bauer’s four-month stint as a prison guard.

In doing so, the magazine walked up to the line of accepted journalism ethics: reporters shouldn’t lie or misrepresent themselves as they pursue a story.

Bauer used his real name and Social Security number in applying for the $9-an-hour job, and said his previous employer was the parent company of Mother Jones, the Foundation for National Progress. But he never let on that he was a reporter, or that he was using recording equipment. (A quick Google search would have revealed that Bauer was famous as one of the American hikers who were jailed in Iran for almost two years from 2009 to 2011.)

“We took these issues very seriously,” the magazine’s editor in chief, Clara Jeffery, told me. But editors decided to go ahead for a simple reason: “We felt there was no other way to cast light on privately run prisons.”

The horrendously short staffing at Winn Correctional Facility in rural Winnfield, La., meant misery for inmates and guards alike.

One prisoner who had lost fingers to gangrene was denied medical care. Inmates attacked and stabbed other inmates. And the prison had no psychiatrist on staff to deal with 1,500 inmates. Brutal force seemed the answer to every situation that arose.

Undercover reporting becomes necessary, Jeffery said, “when it’s about people who don’t get their stories told very often.”

But there are risks, as ABC found out when Food Lion sued. An initial verdict against the network of $5.5 million was reduced to $316,000, and then reduced again to a nominal $2. But the episode cast a long-lasting pall on undercover reporting.

In the late 1970s, the Chicago Sun Times set up a phantom business, the aptly named Mirage Tavern. Praised for revealing how corrupt government inspectors accepted bribes from small-business owners, the Sun Times report was shunned by the Pulitzer Prize board because of concerns about the ethics of a story based on wholesale deception.

Mother Jones went ahead with publication with a legal threat already lodged by the prison’s parent, Corrections Corp. of America. (Notably, it came from the same law firm that represented the billionaire Frank Vandersloot, who sued Mother Jones unsuccessfully a few years ago, and who pledged $1 million to support other suits against the magazine; the situation is reminiscent of fellow billionaire Peter Thiel’s support of legal actions intended to drive Gawker out of business.)

New York University journalism professor Brooke Kroeger, who wrote the 2012 book “Undercover Reporting: The Truth About Deception,” told me she is a believer in this kind of journalism — “but only under very controlled circumstances and for something really important that matters to the public interest.”

She puts Mother Jones’s Louisiana prison reporting in that category, and has added it to the NYU database in which thousands of examples over many decades are collected.

Many mainstream news organizations don’t countenance undercover reporting in any form because they insist that reporters identify themselves as working journalists; The Washington Post is among these.

And for good reason — being truthful is of utmost importance. Misrepresentation, by its nature, works against reader trust. And it’s not fair to those being written about.

But it’s not always a clear-cut line. After all, not much of the best reporting gets clearance through public-relations departments.

Kroeger opens her book with a description of The Post’s investigation into the Walter Reed Army Medical Center, which won the Pulitzer Prize for exposing the deplorable quality of care for war veterans there. While never misrepresenting themselves, Post reporters did get a crucial inside view by staying under the authorities’ radar as they visited families and patients. The investigation brought real reform.

Ted Conover’s book about his undercover experiences as a prison employee, “Newjack: Guarding Sing Sing,” was a Pulitzer Prize finalist in 2001, which may suggest that the journalistic establishment sees the merits of such techniques yet is unwilling to fully endorse them.

Can any form of misrepresentation (even if indirect) be justly employed to serve a larger truth? Failing the counsel of Talmudic scholars, I’ll defer to Conover’s description of undercover reporting: “the nuclear arrow in the writer’s quiver, a potent tool that should be used only with extreme care and in a limited number of cases.”

The best journalism must peel back layers to reveal the truth. As the maxim has it, “News is what somebody somewhere wants to suppress. All the rest is advertising.”

For more by Margaret Sullivan visit wapo.st/sullivan

Correction: This column was incorrect in stating that a Louisiana prison run by Corrections Corporation of America had no psychiatrist on staff for its 1,500 inmates. The prison has a part-time psychiatrist and a part-time psychologist at the facility on a weekly basis, according to CCA.

In addition, the column stated that an inmate with gangrene was denied medical care. The column should have attributed that statement to Mother Jones magazine’s reporting, as well as to a lawsuit that the inmate filed against CCA. The lawsuit is still pending, and CCA has denied the claim.