A loophole in nonprofit law means that corporate lobbying is at least double the official figure

Officially, Americas total 2017 corporate lobbying group spending was $535m, but as much as $675m more was funneled from industry groups to politicians as part of influence campaigns.

Maplight found the off-the-books spending by data-mining the tax returns of more than 100 501(c)(6) nonprofits -- a special tax designation for trade groups, from the US Chamber of Commerce to the Washington State Society of Anesthesiologists.

Nonprofits tax returns are public. By looking for line-items like "'advocacy,' 'consulting,' 'contributions,' 'coalitions,' 'consortiums,' 'government affairs,' 'communications,' 'programs,' 'special projects,' 'dues,' 'memberships,' and 'subscriptions'," Maplight was able to identify influence money that was not counted because it was laundered through other organizations.

For example, the trade group Americas Health Insurance Plans (AHIP) funneled $100m to the Chamber of Commerce to fund anti-Obamacare lobbying, but marked up the funds as "advocacy," not "lobbying."

There's lots of incredibly vague, high-ticket stuff buried in these tax-returns, spending on "other fees for services" and "other expenses," while other line-items are a little more explicit, like "coalition expenditures" ($1.5m, Financial Services Roundtable) "policy research and consulting" ($4m, Chamber of Commerce), "consulting" ($82m, Phrma), "strategic planning" ($9.2m, American Fuel and Petrochemical Manufacturers), etc.

Nonprofits are only required to itemize their other fees for services if they account for more than 10 percent of their total functional expenses, which offers some trade associations an additional avenue for secrecy. For example, since the American Hospital Association listed more than $126 million in total functional expenses in 2017, it didnt need to spell out any of the items included in its $12 million line for other fees for services.

Last year, the health care industry launched the Partnership for Americas Health Care Future, or PAHCF, a 501(c)(4) dark-money organization, to oppose growing momentum for Medicare for All or more limited reforms.