The Charity Commission has been given new powers to covertly photograph suspects such as bogus face-to-face fundraisers. It will also be able to use agents and informants under new investigative powers granted to it by amendments to the Regulation of Investigative Powers Act 2000.
Human rights group Liberty described the new powers as "disturbing" and questioned the need for such intrusive procedures.
In the past, the Commission has been able to use some investigative methods, such as obtaining telephone bills, but only with permission from the user.
"This will enable the Commission to investigate abuses in the charity sector using techniques currently unavailable to our staff," said Paul Fredericks, head of compliance and enforcement.
But Liberty is concerned the powers may infringe human rights. "There was no warning the proposals would be made and no explanation as to why they're necessary," said spokesman Barry Hugill.