Bloomberg gets a great scoop on the Chamber of Commerce, reporting that the health-insurance industry gave the secretive nonprofit a stunning $86.2 million last year to oppose Obama’s health-care reform.

The Chamber, as we’ve seen, isn’t required by law to disclose who its donors are. That ought to change. But meantime, how are journalists supposed to get at that information? Here’s how Bloomberg did it:

The organizations disclosed the funding yesterday in annual tax records required under U.S. law. The Chamber’s records show it received $86.2 million from a single group, which a second person briefed on the transaction by those involved identified as Washington-based America’s Health group.

Insurers gave the $86.2 million to the Chamber in August 2009, funded by health insurers, said the first person. Early that month, America’s Health Chief Executive Officer Karen Ignagni said Democrats were trying to “demonize” insurers.

Nicely done.

How big a number is $86 million? Well, remember how the Chamber said it would spend $75 million mostly opposing Democrats in the midterms—people went nuts over that. This is for a single issue from a single industry. A couple of observers quoted by Bloomberg’s Drew Armstrong call it “breathtaking” and “astonishing.”

But it’s also worth noting how small a number $86 million is in the grand scheme of things. That’s not that much money for a health-insurance industry trying to stave off radical reform. Wellpoint alone earned $4.7 billion last year.

Once again, we see the Chamber serving as a front for an industry to lobby hard for what it wants without anybody knowing it’s doing so. It’s a reputation laundry for issues pushed by loathed industries. Wall Street wants to lobby against financial reform while saying publicly it favors it? Funnel the money to the Chamber. Health-care insurers want to influence the process without having their hated names attached? Do the same.

It shouldn’t take the journalistic shoe leather it did here to get this information to the public. For one thing, it often comes too late, as it did here. But until these massive, secret corporate donations are made illegal or at least brought into the daylight, on shoe leather we’ll depend.

A round of applause is in order for Bloomberg and Armstrong.

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu. Follow him on Twitter at @ryanchittum.