Ikea France has been accused of collecting personal data by fraudulent means and unlawful disclosure of personal information.
Furniture and home goods company employs 10,000 people France and was reported by the unions to the French authorities in 2012.
The unions specifically alleged that the retailer paid for access to police files containing information on targeted individuals.
Ikea France has denied spying on anyone, but the SwedishThe France-based company fired four executives in France after prosecutors opened a criminal investigation in 2012.
A charge alleged that Ikea France used unauthorized data to try to catch an employee who had applied for unemployment benefits but was driving a Porsche.
Another said the subsidiary investigated an employee’s criminal record to determine how capable he was of owning a BMW on a low income.
Customers with whom the company was in dispute were also said to have inappropriately accessed their personal information.
In France, Ikea has 34 stores, an e-commerce site and a customer support center.
Former head of Ikea France’s risk management department, Jean-François Paris, admitted to French judges that 530,000 to 630,000 euros per year (454,600 to 540,400 £) had been reserved for such surveys.
Paris, who is among the defendants, said his department was responsible for managing it.
Former Ikea France CEOs Jean-Louis Baillot and Stefan Vanoverbeke, and former CFO Dariusz Rychert and store managers are also on trial.
If found guilty, the two former leaders face sentences of up to 10 years in prison and fines of € 750,000 (£ 643,300).
Ikea France incurs a maximum penalty of 3.75 million euros (3.2 million pounds sterling). The trial is expected to last until April 2.
The company also faces potential damages from civil lawsuits brought by unions and 74 employees.
In 2012, the retailer said it was cooperating with French law enforcement authorities and had adopted procedures to prevent illegal activity.