What is the difference between required and preferred suppliers?

Although very similar, required suppliers are necessitated by state or university negotiated agreements. These vendors are on university-wide contracts. Preferred suppliers have been properly vetted and comply with all university policy and state requirements. Many of these suppliers have specific departmental contracts and are required for that particular department. The use of these vendors can be extended to the university community. This saves both time and money to the university. Other suppliers can be used if the good or service cannot be found on these preferred agreements.