The Wall Street Journal has an interesting dive into public records, reporting today that unions in the U.S. spend a lot more on politics and lobbying than was known previously. Four times as much. (Click here to read the full story.)

The story by reporters Tom McGinty and Brody Mullins uses reports that unions must file with the U.S. Department of Labor. McGinty is a specialist in the use of databases of public records.

An excerpt:

Previous estimates have focused on labor unions' filings with federal election officials, which chronicle contributions made directly to federal candidates and union spending in support of candidates for Congress and the White House.

But unions spend far more money on a wider range of political activities, including supporting state and local candidates and deploying what has long been seen as the unions' most potent political weapon: persuading members to vote as unions want them to.

The new figures come from a little-known set of annual reports to the Labor Department in which local unions, their national parents and labor federations have been required to detail their spending on politics and lobbying since 2005.

This kind of spending, which is on the rise, has enabled the largest unions to maintain and in some cases increase their clout in Washington and state capitals, even though unionized workers make up a declining share of the workforce. The result is that labor could be a stronger counterweight than commonly realized to "super PACs" that today raise millions from wealthy donors, in many cases to support Republican candidates and causes.

The story is careful to note that we can't know whether unions spend more than corporate interests, which don't have to file such reports.

An interactive graphic with the story lists the 200 unions that reported the most spending on politics and lobbying, starting with the AFL-CIO, airline pilots and air traffic controllers.

The Wall Street Journal is behind a paywall, but you can read this story through a Google News search.

More on recent FEC reports on campaign contributions:

• Pro-Ron Paul PAC misses $$$ deadline, blames credit card company
• After TV cameras leave, Romney Super PAC discloses $18 million
• Casino magnate Adelson's family gave early to Gingrich PAC