The commissioner may refuse to grant a license or may revoke or suspend any license issued under the provisions of this article, for the violation of any of the provisions of this article or of any of the rules and regulations adopted pursuant to the provisions of this article: Provided, That before such suspension or revocation becomes effective the party shall be notified by the commissioner of his intention to refuse, revoke, or suspend and the party shall be given ten days in which to request a hearing before the commissioner, which request shall be made in writing by registered mail. The commissioner is hereby authorized to summon witnesses for and to take testimony at such hearings.