Three senior Ikea executives in France were put under investigation on Wednesday over allegations they spied on disgruntled customers and former staff.

The head of Ikea France is among those accused of employing a firm of private detectives to snoop on individual employees, particularly union activists, job applicants and even unhappy customers, and of fraudulently obtaining personal information from police files.

A judge decided there was enough evidence to formally mis en examen (the equivalent of being charged) Stefan Vanoverbeke, the chief executive of Ikea France, his predecessor Jean-Louis Baillo and chief financial officer Dariusz Rychert, who were arrested on Monday and held for questioning.

Under French law, the men had to be formally put under investigation within 24 hours or freed.

Since January, a total of 10 people have been arrested and put under investigation for "fraudulent use of personal information", including four police officers and Ikea's former head of security.

The case is hugely damaging to the reputation of the flagship Swedish company famed for its family-friendly but infuriatingly difficult to assemble flat-pack furniture.

The accused are said to have requested a range of personal data, including criminal records and confidential details about the targets' dealings with the police or courts, even as witnesses or victims. Scores of people were alleged to have been snooped on, including a union official.

Last year, the satirical magazine Le Canard Enchainé obtained and published emails allegedly between Ikea's management in France and Sûreté International suggesting the security company was obtaining information from the national police information system on behalf of Ikea. The magazine said Ikea agreed to pay Sûreté International €80 (£66) for each request for information and that up to 200 demands were made at the same time.

Two unions have filed legal complaints against Ikea, accusing it of snooping on hundreds of people over a period of at least five years.

Among the claims is that Ikea asked investigators to find out if a customer, who was suing the company for €4,000 (£3,350), owned her own property or was known to the police. Other accusations centre on the tracing of car registration numbers.

Vanoverbek's lawyer, Alexis Gulbin, said his client denied involvement. "It was he who took corrective measures as soon as the problems were detected," Gulbin said.

Ikea France suspended and later fired the head of its risk management department last year along with three top-level executives, before publishing a new code of conduct.

In a statement in 2012, Christophe Naudin, head of Sûreté International, told journalists last year it had "consultancy and security contracts" with Ikea, but flatly denied snooping for the firm.

If found guilty of fraudulently using personal information, the accused face up to five years in prison and €300,000 in fines.