French employers must declare monitoring to the French Data Protection Authority (CNIL) in advance if they want to use evidence obtained from that monitoring in court. The use of the employee’s company mailbox for personal purposes is tolerated under French law, when reasonable. Where it is considered abusive, however, it could constitute a breach of conduct against which the employer may impose sanctions.

Employers generally use monitoring software to discourage and establish evidence of abuse. Such software may be lawful provided the employer follows the rules stipulated by the French Labor Code and the French Data Protection Act to ensure the protection of personal data. In particular, the employer must submit information to and engage in consultation with the works council, provide information to employees impacted by the software, as well as make a formal declaration of the proposed monitoring activities to CNIL – except where a Data Protection Correspondent (Correspondant Informatique et Libertés) is appointed.

These requirements must be met before the implementation of the monitoring software. If these steps are not fulfilled, the software and monitoring activity remains illicit and the employer cannot rely on evidence obtained through that software to establish the employee’s misconduct.

The requirement to comply with the French data privacy law was reinforced by the French Social Supreme Court in a case where an employer’s software monitoring company mailbox flows had detected that an employee had dispatched or received 1,228 personal messages. But the employer’s declaration to the CNIL about the software had been filed after the beginning of the employee’s dismissal process.

The Social Supreme Court ruled that the employer could not use the data collected and, more generally, that any data collected by an automated personal data processing tool prior to its CNIL filing, constitutes an illicit means of evidence.

This decision marks the first time that the French Social Supreme Court has officially ruled that prior declaration to the CNIL is a necessary condition affecting the validity of evidence in this context. This is a similar conclusion and rationale to the 2013 decision where the sale of client files was rendered null and void by the French Supreme Commercial Court for failure to comply with the CNIL registration obligations and demonstrates once again how data protection is becoming a key matter in all legal areas, including employment law.