Of those five, GE (GE) is one of the few companies that openly discloses its federal lobbying expenditures: $15,170,000 in 2014. You can also find links to detailed Congressional filings that cover GE’s lobbying of virtually every government department on a huge range of issues from intellectual property to legislation to B1 Bomber modifications. As one of the largest employers in the U.S, a GE spokesperson tells Fortune, “We have an obligation to shareholders and employees to ensure that their voices are heard on issues that impact our businesses.‎”

If you want to know how much a company you invest in is spending on lobbying at the federal level, you can visit OpenSecrets.org, or if you want to get really granular, go to the Senate and House databases and search yourself. It takes a little time to add up the quarterly filings, but the information is there. Typically, however, that’s the only place it is disclosed.

But these figures underrepresent actual spending because the reported amounts may or may not include contributions to trade associations, which take member money and spend it on lobbying themselves. And the Senate and House figures only include federal-level lobbying, not state-level politicians.

Finding out how much a company spends lobbying politicians at the state level is virtually impossible, except in about a dozen states that require varying levels of disclosure. Among them California and New York require companies to report the data fully. John Keenan, corporate governance analyst at labor union AFSCME, says, “There is no uniform disclosure, and most states leave much to be desired. You have to visit 50 different websites, and when you get there, the disclosure is uneven and spotty.”

One company trying to make state-level disclosure more transparent is Walmart (WMT), which recently announced in response to a shareholder proposal from Zevin Asset Management that it would disclose state spending. But the discount retail giant still will not disclose what it spends on “indirect lobbying,” the portion of the fees it pays trade associations—such as the U.S. Chamber of Commerce—that are used for lobbying, so a full disclosure will still be incomplete.

Starbucks aims for a more open policy on trade association lobbying. The coffee chain does disclose that a portion of the fees it pays to the two trade associations it’s a member of—the Grocer Manufacturers Association and the National Coffee Association of America—are used for lobbying. But it does not disclose what it pays those associations.

According to OpenSecrets.org, Starbucks (SBUX) spent $460,000 on lobbying in 2014. A company spokesperson confirmed that this amount was separate from the portion of trade association fees spent on lobbying. A visit to the Congressional sites confirms this, indicating the work of a lobbyist on climate change, food safety, higher education, veteran and youth hiring, tax, and workplace policies.

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Why should shareholders care? Because in aggregate we’re talking about a lot of money—far more than is spent directly on candidates or contributing to PACs. This is the case even during an election cycle. During the 2010 race, Fortune 500 companies spent $246 million on federal campaign expenditures but spent at least $5.1 billion on federal lobbying, according to a Princeton University study. Further underscoring the significance of lobbying by trade associations, the same study found that for the same period, the U.S. Chamber of Commerce spent $33 million on political contributions and $302 million on lobbying.

Why hasn’t the Securities and Exchange Commission instituted proper disclosure of lobbying expenditures? Back in 2013, a proposed rule was put forward, but corporations reacted with horror and enlisted the support of the Chamber. In addition, says Keenan, “Republicans in Congress have threatened to strip funding from the SEC if they even work on the disclosure rule.”

As with many issues like this, shareholders have had to step into the breach. Around 200 proposals calling for the full disclosure of lobbying expenditures have been filed with companies since 2011 by a large number of shareholders, often acting in tandem. Leading this charge are AFSCME and Walden Asset Management. Shareholders have found success at other large companies besides Walmart, including Apple and Home Depot which both agreed this year to make fuller disclosures, but even when supported by the majority of shareholders, these proposals are non-binding, and companies can choose to implement them only partially. The average level of support over five years is more than 25%, but many individual proposals have received majority support, such as at Sallie Mae and Lorillard.

A spokesperson for the U.S. Chamber of Commerce says it’s fully disclosed all of its lobbying activities, as required by law. “But that is not enough,” the spokesperson says, “for anti-business activists – they have orchestrated a ‘disclosure’ campaign that is really meant to intimidate corporations from participating in important policy debates, either directly or through trade associations and organizations such as the U.S. Chamber.”

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The Chamber also challenges that there is widespread corporate support and/or change for lobbying disclosure, yet almost a quarter of the 200 companies where shareholder resolutions have been filed since 2011 have agreed to make disclosures beyond the requirements, and another 30 saw more than a third of shareholders support the resolutions.

“Secrecy in political spending is not analogous to free speech, reputational risk from undisclosed political spending is real, and shareholders have a right to ensure that boards of directors are monitoring this risk,” says AFSCME’s Keenan.

Timothy Smith, director of ESG shareowner engagement at Walden Asset Management says, “We respect the right of companies to participate in the political process but believe … that we should know how our shareholder dollars are spent.”

The piecemeal shareholder resolution approach, while effective company by company and gaining in effectiveness, is still piecemeal. This is why an SEC solution is needed to make disclosures consistent and complete. The big irony, of course, is that a rule on disclosing corporate lobbying dollars is being blocked because companies are spending dollars lobbying politicians in Congress.