The commission, on proof of violation by a licensee, its agents or employees, of this chapter or any rule adopted by the commission may, on reasonable notice to the licensee and after giving the licensee an opportunity to be heard, fine the licensee or revoke or suspend the license. If the license is revoked, the licensee is not eligible to receive another license within twelve months from the date of revocation. Every decision or order of the commission must be made in writing and filed with the executive director for preservation as a permanent record of the commission. The decision must be signed by the chairman, attested by the executive director, and dated.