Owner Operator Independent Driver Association OOIDA.com is one I belong to. The American Trucking Association is the industry trade group that represents many/most of the big trucking companies. I don’t know of others, off-hand.
OOIDA has some decent benefits, especially for very small fleet companies and single truck owner-ops. One benefit I like is they will review your lease before you lease on with a company or before you start a Lease-Purchase agreement with a company. They will read through the lease and go over it with you, line by line, and point out where the company makes you PROMISE to do X and they agree to TRY and do Y. Membership is $49/yr.