Leicester City Council fraud investigators have accessed staff members' email and internet records more than 30 time since April last year.
The council's latest annual counter-fraud report says it sought permission 33 times to look at employees' computer use.
Investigators were looking into cases of cheque manipulation, counterfeiting, theft, employees carrying out private work on the city council clock or while on sick leave and corruption surrounding contracts and the misuse of council facilities.
The report said: "The (counter-fraud) team has made unannounced visits to council premises to secure evidence including data held on digital devices .
"Team members have interviewed employees, members of the public and contractors.
"They have liaised with police over potentially criminal matters."
The report does not give specific details of the results if the inquiries.
