The government has promised curbs on council spying
Councils in England and Wales have used controversial spying laws 10,000 times in the past five years, figures obtained by the Liberal Democrats show.
The Regulation of Investigatory Powers Act (Ripa) was designed to fight serious crime.
But officials have been using it to spy on suspected dog fouling, littering and other minor offences.
The government has promised curbs on its use but the Lib Dems warn it could still become a "snoopers' charter".
The figures, obtained under the Freedom of Information Act, reveal for the first time how widespread the use of Ripa is among council officials in England and Wales.
A survey of more than 180 local authorities found:
• 1,615 council staff have the power to authorise the use of Ripa.
• 21% (or 340) of these staff are below senior management grade.
• Ripa powers have been used 10,333 times in the last five years.
• Just 9% of these authorisations have led to a successful prosecution, caution or fixed-penalty notice
The Lib Dems are calling on the government to ensure that Ripa powers are only used where strictly necessary and that their use is sanctioned by magistrates.
The party's local government spokesman Julia Goldsworthy said: "This government has seen civil liberties as little more than a temporary inconvenience.
"Slowly but surely freedoms have been eroded and we're now in a situation where dog fouling is considered sufficient to warrant surveillance by council officials."
Shami Chakrabarti, of civil rights campaign group Liberty, called for tighter restrictions on the use of surveillance powers.
She told BBC News: "The over-use of surveillance is destroying trust in proper law enforcement."
Council officials were even using "targeted surveillance," including monitoring phone calls, e-mails text messages and CCTV, to police school catchment areas, she added.
The government is planning to issue new guidelines to councils on the use of Ripa.
Local government minister John Healey has written to councils to emphasise that the powers are "not appropriate" for tackling offences like littering or dog fouling.
"It is right and important that councils have these powers of surveillance," he said, as an effective weapon against rogue traders, fly tippers and loan sharks.
But he added: "The public must have confidence in who has these powers and that they are used in a proportionate and proper way."
Ministers want applications for the use of Ripa to go to the top of organisations, such as the chief executive of a council rather than the head of trading standards or environmental health.
The Conservatives say they would restrict the use of Ripa powers by local authorities only to crimes which could lead to a prison sentence.
Local councils would also require judicial approval for the use of surveillance powers and council leaders would have to sign off each use of the powers, under Tory proposals.