Democratic House and Senate candidates seem likely to lose the votes of a large constituency they rarely think about over a law that most Americans have never heard of.

The issue is FATCA — the Foreign Account Tax Compliance Act — passed by Congress and signed into law in 2010. The provisions of the law, which took effect this summer, are complicated, but as the Wall Street Journal explained this month: “FATCA requires foreign financial firms to give the Internal Revenue Service information about the investment income and account balances of many of their U.S. customers. Steep financial penalties apply to individuals who don’t comply with complex tax-reporting rules.”

Intended to crack down on wealthy tax cheats with hidden foreign accounts, the law is having ruinous — and apparently unintended — consequences for a large number of ordinary low- and middle-income U.S. citizens living abroad. European banks are refusing to accept American customers. American investment firms are refusing to let U.S. citizens living abroad trade securities. American-born workers with fiduciary responsibilities are losing their jobs. The reporting burdens placed on foreign financial institutions could even have long-term negative effects on the U.S. economy.

One American whose life has been turned upside down by FATCA told her story recently in Forbes magazine in a story headlined “Giving Up Citizenship Because of Taxes.” Tisha, a typist and small-business owner, moved to Europe to take care of her ailing mother. She had always been proud to pay her taxes and says she never would have considered giving up her U.S. citizenship to avoid them. But then came FATCA and the tax complications that followed her mother’s death. Now past 60, she sees renunciation as the only solution to her problems.

“So will I renounce to avoid taxes?” she wrote. “Not exactly, because I don’t owe taxes due to my very low income. But in order to avoid the constant threat, like a huge hammer hanging over my head, of ‘information filing penalties’ as I grow older and less able to cope. To protect my executors from those same things? Yes, I’m afraid I shall have to.”

As sad and appalling as stories such as this are, it’s even worse when you consider that FATCA applies to many “U.S. persons” who have never lived in the United States — “border babies” born to Canadian parents in U.S. hospitals, for example, and people born overseas who acquired U.S. citizenship from their American-born parents.

The group Republicans Overseas has called for FATCA’s repeal, and the GOP has put a call for repeal in its platform. Democrats Abroad has proposed what it calls the “same country exception,” which would exempt those Americans who live abroad and do their banking in their country of residence. That would be an improvement; most of those affected by the law are not rich Americans hiding their assets offshore but ordinary people doing business at the bank down the street.

But the Democratic Party is standing staunchly behind its legislation and shows no sign of willingness to change. This has not escaped the notice of American expatriates, many of whom would otherwise be natural supporters of the Democrats.

“Remember this in November. I was once a staunch and loyal Democratic voter and campaigner. Never again,” one expat wrote on a recent Wall Street Journal blog. “The Democrats created FATCA, Obama signed it into law and they insist on keeping it, so they must and should pay the price. Not one Republican voted for FATCA back in March 2010. It was a total Democratic Party creation, from start to finish. Spread the word to your families and friends in the U.S. To stop FATCA, do not vote for any Democrat in the upcoming elections in November and not until this insult to ‘fair laws’ is abolished completely.”

Another wrote: “I, too, was once a ‘loyal’ Democrat, but as an expat living abroad, this FATCA nightmare has made me open my eyes. I wrote to three Democrat senators and only received a standard reply from one. I called four Democrat congressmen and was told by one, ‘You and your husband should return to the U.S. and you won’t have the problem with FATCA anymore.’ He then laughed and hung up. I have had two investment accounts closed and am threatened that our joint checking and savings account will be closed, as well. None of this is a secret, and there are articles about this everywhere. I, too, ask, Why is no action taken?”

FATCA may be “the worst law you never heard of” for most Americans, but for those living abroad, it is an increasing threat to their financial well-being. It’s beginning to look as though the votes of those Americans, which could be crucial in close races, will not be going to the party of FATCA, even if that means they won’t be voting at all.

Bob McIntosh was an editor at the Pioneer Press from 1981 to 2006. He lives in Victoria, British Columbia.