Should a temporary employee benefit from the PEPA bonus set up by the user company?

Ms [U], a temporary employee of the FED finance temporary employment agency, carried out temporary assignments from April to December 2018 with Allianz Vie.
Allianz Vie introduced an exceptional purchasing power bonus for its employees. In its unilateral decision of January 23, 2019, the user company stated that employees on temporary contracts at December 31, 2018 were not concerned by the measure.