A. There is hereby assessed a fee to be determined by each oilseed subcommittee for oilseed marketed by oilseed producers in this state and sold or handled through commercial channels. The fee shall be assessed and imposed upon the oilseed producer at the time of sale or delivery and shall be collected and remitted by the first purchaser to the Oklahoma Oilseed Commission. Pursuant to the provisions of the Oklahoma Oilseed Resources Act, no oilseed shall be subject to assessment of a fee more than once including a national checkoff. If the assessment of a national checkoff fee ceases to exist, an Oklahoma assessment shall then be implemented.