Americans for Prosperity Foundation Chairman David Koch addresses attendees of the Defending the American Dream Summit in Orlando, Fla., Friday, Aug. 30, 2013.(AP Photo/Phelan M. Ebenhack)

A Koch spokeswoman recently called the brothers' spending "drops in a bucket" compared to what unions spend.

The comparison suggests just how powerful the Kochs really are. To make their influence seem small, the two brothers, their corporation and a couple hundred of their allies invite comparison with 14.5 million American dues-paying union members.

But even when stacked against all of organized labor, the political spending of the Kochs is plenty more than just drops in a bucket. It amounts to at least one-quarter of all union spending.

An analysis by The Huffington Post found that labor unions spent more than $1.7 billion on politics and lobbying in the 2012 election cycle. The Koch network spent at least $490 million in the period. No single union came close to matching the Kochs' spending. The union spending total is probably slightly overstated in this analysis due to some double-counting of expenses.

Data comes from the Department of Labor, Internal Revenue Service tax forms, Center for Responsive Politics and National Institute for Money in State Politics. Totals are rounded.

The labor total comes from disclosure reports unions are required to file with the Department of Labor, along with data on political contributions made by unions' political action committees. The Labor Department filings include disclosures on educational and issue-based spending that go far beyond what's required by campaign finance laws.

In an attempt to compare the Koch and union disclosures as closely as possible, the Koch network total includes the $407 million spent by the Koch political network and detailed by the Center for Responsive Politics; the $39 million spent by American for Prosperity Foundation, a 501(c)(3) nonprofit chaired by David Koch; charitable donations made through Koch foundations to political issue and education groups; federal and state campaign contributions from Koch Industries' political action committees and employees; and available federal and state lobbying.

The $490 million total is almost certainly a low estimate, because the Kochs operate an "intentionally confusing network of nonprofits," said Center for Responsive Politics researcher Robert Maguire.

Jeff Hauser, a spokesman for the AFL-CIO labor federation, said labor unions serve as a political counterweight to the Koch brothers and other business lobbies, but only in terms of grassroots reach. When it comes to pure finances, organized labor is "dwarfed" by business, Hauser said.

"We're significant because we have millions of members who have many non-union friends and family members. So the reach of the labor movement and its ability to do door-to-door, talking in neighborhoods -- that's a significant counterweight to plutocrats simply buying legislation," Hauser said. "But we can't compete dollar for dollar."

As for the spending by the Kochs and their affiliates, "It's really revolutionary in the worst possible sense of the word, and it's why they need to create a labor bogeyman," Hauser argued.

Koch Industries spokesman Rob Tappan called comparisons between Koch and union money "apples-to-oranges" because "Charles Koch and David Koch spend their own money."

"Unions spend their members’ money, at times against their interests and individual preferences," Tappan said.

Political spending by labor unions was the subject of a panel at last week's Conservative Political Action Conference, the annual Washington gathering of right-wing elites. While celebrating the spread of right-to-work laws that undermine organized labor, anti-tax and anti-union crusader Grover Norquist claimed unions are "the largest political player in American politics and will be for some time."

Unions may wish that were the case. While organized labor spends more money than the well-funded network operated by the Kochs, union spending is a tiny fraction of the total amount that business interests spend to influence politics.

All business sectors combined to spend at least $9.5 billion to influence politicians at the federal and state levels in the 2012 election cycle, including campaign contributions and lobbying. Labor unions spent $600 million.

Data comes from Center for Responsive Politics and National Institute for Money in State Politics.

These totals come from Center for Responsive Politics data on federal campaign contributions and federal lobbying, and National Institute for State Money in Politics data on state campaign contributions, including ballot initiatives. (State lobbying disclosure laws aren't uniform enough to provide a total number.)

Union spending "pales in comparison to right-wing corporate interests," said Brian Weeks, political director for the 1.6-million member American Federation of State, County and Municipal Employees. "It's not even close. And let's be honest -- when they're talking about union money, they're talking about our members -- librarians, snow plow drivers, park rangers."

The full scope of business spending on politics is impossible to quantify. If corporations and executives were required to comply by the disclosures that unions do, there would likely be billions more in political and lobbying expenses in their names. All union spending is already known.

Labor's $600 million still trails a number of business sectors when they are broken out individually. The most powerful business sector is finance, insurance and real estate, which spent $1.9 billion on federal lobbying, and on federal and state contributions in 2012 elections.