WASHINGTON, April 14 (UPI) -- Public Citizen said it filed suit in Washington Thursday against the Internal Revenue Service for allegedly illegally hiding some of its operations.

The suit, filed on behalf of the Transactional Records Access Clearinghouse, says the IRS wrongly claims without substantiation some of the unclassified information would compromise homeland security if released to the public.

The IRS for many years has released scores of statistical tables and other information that allowed the public, Congress, tax lawyers and other interested parties to make their own judgments about how the agency is enforcing the tax laws, the organization said.

But now the IRS is refusing to make public much of this information, Public Citizen said.

The non-profit watchdog group said researchers used the information in the past to demonstrate, for example, that wealthy taxpayers are much more successful than poor ones when it comes to reducing the amount of taxes and penalties the IRS initially claimed they owed in enforcement actions.