British North America Act, 1867, S. 92A(4)

(4) In each province, the legislature may make laws in relation to the raising of money by any mode or system of taxation in respect of 
(a) non-renewable natural resources and forestry resources in the province and the primary production therefrom, and 
(b) sites and facilities in the province for the generation of electrical energy and the production therefrom,

whether or not such production is exported in whole or in part from the province, but such laws may not authorize or provide for taxation that differentiates between production exported to another part of Canada and production not exported from the province.

Documents related to section 92A(4)