When the IRS wants to snoop, it calls on a secretive and little-known investigative unit—undercover g-men authorized to pose as lawyers, doctors, journalists, or even priests to gain the trust of targets and gather evidence against them. This building is where the tax collector's spies work.

The Ted Weiss Federal Building, located at 290 Broadway, near City Hall in downtown Manhattan, furnishes office space to the IRS (on the lower floors) and the Environmental Protection Agency (on the upper ones). Take one of its elevators to the fourth floor, and you’ll arrive in a small, windowless hallway belonging to the agency’s Criminal Investigative Division.

The floor has no front desk, no receptionist, and minimal markings. At each end of the hallway stand two sets of identical and heavily locked doors.

The existence of the IRS’s crime bureau, and specifically its outpost in New York, has long been known. Its undercover division is not a closely held secret, either. But the size and scope of these covert operations has quietly increased over the years—to a point where 10 percent of the IRS’s roughly 2,500 agents in 2014 were serving undercover, running hundreds of operations a year. One Justice Department source told Gawker that as many as 300 special agents have worked undercover in the past five years, with over 100 permanently in undercover status.

In November 2014, the New York Times reported that the IRS has assigned undercover status to more and more employees—in which capacity they possess the ethically and legally dubious mandate to pose as friends, priests, and even journalists in order to gather evidence against suspected tax evaders. Though the IRS denies using undercover agents posing as journalists, priests, lawyers, or doctors “specifically to gain information from a privileged relationship,” it’s refused to say whether agents posing in those roles have obtained information that wasn't “privileged.” One former IRS supervisor confirmed to the Times that agents had pretended to be doctors “to gain the trust of a medical professional and develop evidence that is tightly held.”

IRS undercover work is listed as one of the general features of criminal work in agency job announcements. What’s weird is that undercover units (of which there are at least four, including the one in Manhattan) are not even mentioned in the IRS budget submitted to Congress. Instead, one line in the fiscal 2016 budget referring to the function of the Chief Counsel says that the office oversees “highly sensitive undercover operations.”

They're not just seeking out tax cheats, either. The undercover unit has focused in particular on crimes related to terrorism and drugs—not traditionally the emphasis of the Department of Treasury—and worked closely with undercover operations at a dozen other federal agencies, including the FBI, DEA, and ATF.

What hasn’t been revealed is the precise location of the New York office that conducts such operations. There are a number of potential locations where the IRS could theoretically place this office—including within its well-publicized counter-terrorism office in Garden City, Nassau County. But according to former I.R.S. employees, the agency’s local undercover unit resides within the criminal division at 290 Broadway, on the very same floor, to which I schlepped earlier this week.

I ended up spending two hours outside the building, waiting on line with taxpayers who either wanted to file their taxes in person or whose federal refund had been withheld for some reason. Inside were security guards manning a temporary TSA-style security checkpoint; to pass through it I had to remove my shoes and belt, just like at an airport. (This setup isn’t typical of federal buildings; apparently the IRS erected the checkpoint in response to the heavy influx of New Yorkers seeking tax preparation help.) Beyond the security barrier, just off a light-filled lobby tiled in marble, were the building’s elevators.

The fourth floor, when I stepped onto it, was completely empty. Along the walls of the hallway are hung pictures of old New York:

And on the locked doors, the New York field office’s insignia:

And that’s pretty much it. After I dawdled for a few minutes, two I.D.-carrying IRS employees, a man and a woman, suddenly appeared—the man from the same elevator I’d disembarked, and the woman from behind one of the locked doors. I asked both of them where I could find the undercover unit, to which they returned identical expressions of bewilderment. The male employee quickly left, but the female employee said she would see what she could do, and eventually returned with a Post-It note containing the name and number of an IRS media specialist (i.e., a spokesperson). A voicemail left with that number on Tuesday was not returned.

Anyway: Happy Tax Day! Now you know a little bit more about where your dollars go.

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