Article L4122-1 of the French General Code of Local Authorities
The territorial boundaries of the regions shall be amended by law after consultation with the regional councils and departmental councils concerned. The modification of the territorial boundaries of the regions may be requested by the regional councils and departmental councils concerned. However, when a decree of the Conseil d’Etat modifies the territorial boundaries of adjacent départements not belonging to the same region, and a favourable opinion has been issued by…