The Secretary may contract with travel service providers, or with a single provider, to acquire travel services for State employees traveling on official business. Upon written notification of the Secretary to the unit head, employees shall book all airline, railway, and ship travel, all car rentals, and all lodging reservations through the State travel service contractor, except under the following circumstances: An unusual situation makes it impractical or impossible to use the services of the State travel services contractor; The State travel services contractor does not serve the area where the employee is located; Travel arrangements are to be made for the employee by the organizer of a planned conference, convention, or seminar in order to obtain special discounts not available through the travel services contractor. When changes in travel planning require cancellation or revision of common carrier tickets, or car rental or lodging arrangements, the employee shall notify the travel services contractor as soon as possible so that the necessary changes can be made.