However, employees who have access to the compensation information of other employees or applicants as a part of their essential job functions cannot disclose the pay of other employees or applicants to individuals who do not otherwise have access to compensation information, unless the disclosure is (a) in response to a formal complaint or charge, (b) in furtherance of an investigation, proceeding, hearing, or action, including an investigation conducted by the employer, or (c) consistent with the contractor's legal duty to furnish information. Knowledge of the theories and practices of vocational rehabilitation counseling; case work principles, practices, and techniques; professional ethics relating to vocational rehabilitation counseling; vocational rehabilitation process as it relates to purchase of services for clientele; and methods of data collection and analysis.