"To work in the network systems development and support area, employees must hold at least one industry-recognized network security credential." Would this be considered a policy or a guideline?

Policy.

Explanation:

A policy is a set of of idea or plan of what to do in particular situations that has been agreed on by a group of individuals, a business organization etc.

A policy is a deliberate system of principles to guide decisions and achieve rational outcomes. A policy is a statement of intent, and is implemented as a procedure or protocol. Policies are generally adopted by a governance body within an organization. Policies can assist in both subjective and objective decision making.