Anyone can request information from U.S. officials under the Freedom of Information Act, a law designed to allow people to know what their government is up to.

When a government agency withholds information from a requester, it typically must invoke one of nine FOIA exemptions that cover everything from national security to personal privacy. But among that list is an exemption—known as b(3) for its section in the FOI Act—that allows an agency to apply other statutes when denying information requests.

Some of those statutes allow exemptions that seem quite reasonable, for example to protect medical or financial information. Many others are more puzzling.

Citing the Watermelon Research and Promotion Act, for example, the U.S. Department of Agriculture has withheld lists of watermelon growers.

Under another law, information about the location of “significant” caves has been withheld by USDA and the U.S. Department of the Interior.

Until now, no one has known just how extensively these other laws were used across the federal government. New data compiled by the Sunshine in Government Initiative, a coalition of journalism and transparency groups, shows that agencies have applied more than 240 other laws in withholding information over the last decade.

And you can see them for yourself: We’ve created an interactive database of all the exemptions used in 2008-2009 and how they were used.

“FOIA is supposed to be a disclosure act, and these b(3)s make it more of a withholding act,” said Patrice McDermott, director of another transparency group, openthegovernment.org. “They can have a detrimental effect to know what government’s doing and hold it accountable.”

For years such provisions could be easily slipped into legislation without notice. But changes to FOIA that went into effect in 2009 require that proposed legislation must specifically say that it will create a new b(3) exemption. As part of their annual FOIA reports, agencies are now required to disclose not only which exemptions they used but also how many times each was invoked.

Financial reforms passed last year by Congress included an exemption to withhold from the public information concerning “surveillance, risk assessments or other regulator and oversight activities.”

The exemption became law, but it was later rescinded after it came under fire by transparency groups.

Our analysis also found that the most-often-invoked exemption is a law protecting information on tax returns filed with the IRS. From 2008 to 2009, federal agencies applied this statute nearly 3,000 times in FOIA denials.

The agency that invoked the most b(3) exemptions was the Department of Veteran Affairs, which from 2008 to 2009 received nearly 170,000 FOIA requests and invoked b(3)s more than 8,000 times—almost always for information relating to Veteran medical benefits or records.

The b(3) exemption used most widely—20 agencies applied it—was a law protecting losing contract bids.

Federal agencies are required to file annual reports about their FOIA activities, such as the number of requests they received, how many they denied and why they denied them. Agencies also must list which b(3) exemptions it used over the past year. Since 2008, reports must include the number of times each exemption was invoked.

“These should be debated and subject to scrutiny,” said McDermott, whose organization, openthegovernment.org, pushed for the disclosure requirement.

There may be legitimate reasons to withhold certain information, she said. “But blowing holes in the Freedom of Information Act is not the way to deal with it.”

View our interactive database of all the exemptions used in 2008-2009 and how they were used.