Does my employer have the right to record my calls in a call centre?

An employee has recently been employed to work in a call centre. His role is to prospect and to expand the customer base of the company.

During a conversation with a prospective client, the employee raises his voice, as the person does not clearly understand the value of the proposed contract. 

The team leader sees him a few days later, and reproaches him for his behaviour. Astonished, the employee learns that his telephone conversations were recorded. He is outraged by this and threatens to go and see a lawyer if he does not receive an immediate explanation

The employer tells him that these records are on the one hand used for internal quality, on the other hand for obtaining evidence at the conclusion of oral contracts. He made enquiries, however, with the person responsible for the data protection as to what precautions and measures to use to comply with the law, which he had failed to do previously.

The employer rapidly explained the new process to his staff one week before the quality control, informing  the  employees that their conversations may be recorded.  In addition, a signal light is activated on the phone when the conversation is actually being recorded. Employees may trigger the recording of conversations themselves, when it leads to the conclusion of a contract. They  must  inform customers that conversations may or will be recorded. Recordings are destroyed one month after the conclusion of the contract.