The French branch of Swedish retailing giant Ikea went on trial Monday accused of running an elaborate system to spy on staff and job applicants using private detectives and police officers.

Ikea France is being prosecuted as a corporate entity along with several of its former executives in Versailles, southwest of Paris.

Journalists uncovered the surveillance scheme in 2012 and magistrates began investigating after the Force Ouvriere (FO) union lodged a legal complaint.

Prosecutors say Ikea France collected details on hundreds of existing and prospective staff, including confidential information about criminal records, as part of a "spying system".

The firm sometimes targeted union members and their representatives, prosecutors allege.

"This trial must set an example," said Adel Amara, a former FO union rep at an Ikea store.

Ikea France, which employs 10,000 people, faces a fine of up to 3.75 million euros ($4.5 million).

The 15 people being tried in the court include former store managers and top executives such as former CEO Stefan Vanoverbeke and his predecessor, Jean-Louis Baillot, who were both present on Monday.

The group also includes four police officers accused of handing over confidential information.

The charges include illegally gathering personal information, receiving illegally gathered personal information, and violating professional confidentiality, some of which carry a maximum prison term of 10 years.

"We're here to today to show that there are these types of actions inside companies that police trade unions and above all their employees," a senior member of the hard-left CGT union, Amar Lagha, told reporters.

 'Get rid of that person'

Jean-Francois Paris, Ikea France's former director of risk management, was allegedly at the heart of the system.

Prosecutors say he regularly sent lists of names to private investigators, whose combined annual bill could run up to 600,000 euros, according to court documents seen by AFP.

The court is investigating Ikea's practices between 2009 and 2012, but prosecutors say they started nearly a decade earlier.

Among the targets was a staff member in Bordeaux "who used to be a model employee, but has suddenly become a protester", according to an email sent by Paris.

"We want to know how that change happened," he said, wondering whether there might be "a risk of eco-terrorism".

In another case, Paris wanted to know how an employee could afford to drive a brand-new BMW convertible.

Such messages usually went to Jean-Pierre Foures, the boss of surveillance company Eirpace.

He would then send Paris confidential information, which prosecutors say he got from the police database STIC with the help of the four officers.

Prosecutors say the information flow may even have gone both ways, with an internal Ikea France document recommending handing over its report about an employee to police "to get rid of that person via a legal procedure outside the company".

Emmanuel Daoud, a lawyer for Ikea France, rejected the spying accusations, but acknowledged that the case had revealed "organisational weaknesses".

He said the company had since implemented an action plan, including a complete revamp of hiring procedures.

"Whatever the court rules, the company has already been punished very severely in terms of its reputation," he said ahead of the trial.

Founded in 1943, Swedish multinational Ikea is famous for its ready-to-assemble furniture, kitchen appliances and home accessories which are sold in around 400 stores worldwide.