The flat-pack furniture firm has also been accused of spying on irate customers.
Without referring to specific cases, the company pledged on Friday to clean up its act.
”Ikea totally condemns the practices brought to light which contravene its must fundamental principles, especially the right to privacy," news agency Reuters quoted Ikea as saying in a statement.
"These practices go against the ethics of Ikea which call for its activities to be conducted in an upright and honest manner.”
Weekly French newspaper Le Canard Enchaîné reported at the end of February that the company used French security companies to gain access to documents held in the STIC system.
STIC (Système de traitement des infractions constatées) is a centralized records system which groups together data from police investigations, including both suspected criminals and their victims.
Accessing the documents without authorization is an offence.
"The allegations have come to our knowledge and we look very seriously upon it. We have started an internal investigation to find out if there is any truth to it," Ikea's Sweden-based spokesperson Ylva Magnusson told The Local at the time.
A series of internal emails published by Le Canard Enchaîné allege that, starting in 2003, the head of security at Ikea's French operation regularly asked for checks on employees and clients.
Questions were asked about more than 200 people, including requests for criminal records, vehicle registration checks and affiliations with political organizations.
In one email reported by the newspaper, the head of risk management at Ikea asked whether a client involved in a dispute with the store was "known to police" and asked for a check on her address.
Another email reportedly requested information on someone who was thought to have made "anti-globalization remarks" and could even be an "eco-terrorist risk.
In mid-March, French police searched the headquarters of the company in France and the home of the employee responsible for Ikea's risk management policy, following fresh allegations that the company had carried out illegal surveillance on dissatisfied customers.