La. Stat. tit. 33 § 118
In any municipality located in a parish which has a parish planning commission, the legislative body of the municipality may designate the parish commission as the municipal planning commission. Upon such designation the planning commission shall have all the powers and functions relating to making, adopting, amending, and adding to the master plan of the municipality or part thereof, or relating to the planning of the municipality as provided or granted by this Sub-part or by other laws to the municipal planning commission of the municipality; and the master plan, its parts, amendments, and additions made and adopted by the designated commission for the municipality shall have the same force and effect in the municipality as though made and adopted by a municipal planning commission appointed by the municipality. In acting as the planning commission of the municipality, the designated parish commission shall follow the procedure specified by the provisions of this Sub-part and other laws relating to municipal planning commissions. Any municipality so designating a parish planning commission as its planning commission shall pay to the designated commission that portion of the expenses of the designated commission which is properly chargeable to the planning service rendered to the municipality.
La. R.S. § 33:118