In order for construction contractors to buy building materials exempt from tax they must receive both an authorization letter and exemption certificate from an exempt entity. Before issuing the authorization letter and exemption certificate, the exempt entity must register the project through the Department of Revenue’s online system and wait to receive approval. Unless the appropriate exemption certificates are issued, construction contractors are required to pay sales and use tax on all purchases of building materials for new construction, reconstruction and alteration except for wind energy conversion equipment. (Iowa Department of Revenue, Tax e-News, April 2, 2004)