The ex-boss of France Télécom and two former executives have been jailed over a restructuring policy linked to suicides among employees in the 2000s.
Didier Lombard was jailed for a year, as were Louis-Pierre Wenès and Olivier Barberot, although eight months were suspended.
The company, since renamed Orange, was fined €75,000 ($83,000; £64,000).
The court examined 39 cases of employees, 19 of whom had taken their own lives and 12 who had attempted to.
The others had lived with depression or had been otherwise unable to work.
It happened during a major restructuring of the company that affected thousands of employees.
Four other executives were found guilty of complicity and given four-month suspended sentences and €5,000 fines.
Lombard, the former president and chief executive officer; Wenès, his deputy; and Barberot, the former director of human resources, were also given fines, of €15,000.
Lombard's lawyer, Jean Veil, said his client would appeal against the conviction.
It is the first time that a French court has recognised "institutional harassment".
The BBC's Paris correspondent, Hugh Schofield, says the trial has been seen in France as a landmark case for relationships between workers and management.
Jean Perrin, whose brother Robert took his own life in 2008, expressed satisfaction at the verdict, but told Libération: "They never had any remorse during the trial; they constantly put the blame on subordinates. I have only disgust and contempt for them."
'Through the window'
At the time, the newly privatised company was in the throes of a major reorganisation. Lombard was trying to cut 22,000 jobs and retrain at least 10,000 workers.
Some employees were transferred away from their families or left behind when offices were moved, or assigned demeaning jobs.
"I'll get them out one way or another, through the window or through the door," Lombard was quoted as telling senior managers in 2007.
He accepted that the restructuring had upset employees, but rejected the idea that it had led to people taking their own lives.
Among the cases documented:
- In 2009, a woman aged 32 took her own life at work in Paris
- A woman tried to kill herself in the eastern city of Metz on learning that she was about to be transferred for the third time in a year
- In 2011, a worker aged 57 killed himself as he arrived at work near Bordeaux
For help and support on mental health visit the BBC Advice pages.
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