The Charity Commission has used controversial powers to obtain information about people eight times since 2004.
The Regulation of Investigatory Powers Act was introduced in 2000 to control investigations by public bodies to fight crime and terrorism.
The act, described as a 'snoopers' charter' by critics and opposition politicians, allows organisations to intercept communications and carry out surveillance.
It could initially be invoked by only nine organisations, but now almost 800 public bodies can use it.
Since the commission acquired powers under the act by an order made in 2003, it has used the communications powers twice in 2004, three times in 2005 and three times in 2007, according to details obtained by Third Sector under the Freedom of Information Act. It has not yet used the surveillance powers.
On five occasions the regulator used the powers to obtain information about people from telephone numbers that had come up during its investigations; twice to obtain information about people from email addresses; and once to obtain details of mail redirection.
A commission spokeswoman said its powers under the act extended beyond fighting terrorism. "That said, although it is exceedingly rare, charities are not immune from terrorist connections," she said.
But revealing further details about its use of the act "could compromise the commission's ability to tackle effectively the very rare but more serious and organised forms of charity abuse", she said.
Belinda McKenzie, coordinator of pressure group the Association for Charities, said she opposed the act but was reassured that the commission had used it only eight times. However, she said this raised questions about the commission's dual role of regulator and adviser.
"Every time it intervenes, it sets off alarm bells in the minds of charities," she said.
Jenny Willott, the Liberal Democrat spokeswoman on the third sector, said public bodies did not have a good record of applying the act correctly.
"I'm relieved to see that there have been few uses of the powers by the Charity Commission," she said.