FORTUNE — It was enough to make anyone from a big company want to crawl under his chair. Here was David Crosby of the Crosby, Stills & Nash folk rock group holding forth at a recent performance in New York City’s Beacon Theatre, not about war or poverty but about corporate power and General Electric. “Can you believe that some big corporations paid no income tax?” he declaimed. “In fact, GE paid no taxes last year.” Then Graham Nash chimed in, “Not only that, GE got a $3.5 billion giveback.” Someone from the audience, in which one-percenters were amply represented — who else could afford the tickets? — shouted out, “Play music.” The group promptly launched into its new song: “They want it all, they want it now.” You can figure out who “they” are.

Talk to big companies about the sentiment expressed by Crosby and Stills, and they whine, feel aggrieved, and carry on about “class warfare.” But as we’ll soon see, they won’t do anything to help themselves.

In fact, Crosby’s rant about GE (which declined comment) is based on a March New York Times story that’s inaccurate. Many public policy types make the same mistake the Times did, conflating the “current tax” number that companies use to calculate earnings with the amount of tax they pay; however, the tax-incurred number isn’t the same as “current tax,” and it isn’t public.

All those mistaken numbers have taken on a life of their own. But do you know whose fault it is for the mistake’s continuing to resonate? It’s the companies’ fault for being stubborn and prideful and refusing to provide information to disprove what they say are false allegations.

Earlier this year professor Ed Outslay of Michigan State University, a leading tax expert, generated no fewer than 16 tax metrics for a GE story that I was pursuing in partnership with Jeff Gerth of ProPublica. However, despite having all those numbers, Outslay couldn’t tell us how much federal income tax GE incurred in any given year or over any given period. Neither can Robert McIntyre of Citizens for Tax Justice, one of Washington’s most respected tax mavens. In a recent study McIntyre — who is way too astute to confuse the “current tax” number with “taxes incurred” — went through the agonies of the damned to calculate how much tax 280 big companies had paid over the past three years. (His study is here.) He devoted special attention to GE, and thinks he has the numbers right. But there’s no way to know.

During the past few months I’ve repeatedly asked three big companies in the tax-wars cross hairs — GE (GE), Verizon (VZ), and Exxon Mobil (XOM) — to voluntarily disclose information that would refute allegations that they incurred no U.S. federal income tax for 2010. All have refused, saying they won’t disclose anything not legally required. They still manage to complain about the allegations, however. I suspect that if I called the rest of the Fortune 500, I’d get 497 similar responses.

As a society, we need the “taxes incurred” information to inform our current tax debate. Investors, too, would benefit; knowing the tax that companies actually incur would be a useful analytical tool.

The solution, as I’ve said before, is for the Financial Accounting Standards Board to require companies to disclose information from their tax returns for the most recent available year and the nine years before that. This information, from lines 31 and 32 of their returns, would take at most one person-hour a year per company to provide. Adding a 17th tax metric to the 16 already available hardly seems like an invasion of corporate privacy.

FASB told me in September that it does not require publicly traded companies to disclose “taxes incurred” information because it hadn’t been asked to require it. Bloomberg View has since joined me in asking informally, and McIntyre says he’ll submit a formal request soon.

If companies are truly getting a bum rap, as they claim, disclosing this information will save them from themselves. And from Crosby, Stills & Nash too.

This article is from the December 12, 2011 issue of Fortune.