Which document would you consult for federal tax requirements?

The correct choice is IRS Publication Circular E, which serves as an essential resource for understanding federal tax requirements. This publication provides comprehensive guidelines on the various federal employment tax obligations that an employer must adhere to, including information on withholding taxes, social security taxes, and federal unemployment taxes. It is particularly useful for contractors and businesses because it details how to accurately calculate and report these taxes, ensuring compliance with federal regulations.

While other documents, such as an employee handbook or job site safety manual, may provide vital information regarding workplace policies and personnel guidelines, they do not address federal tax requirements. Similarly, a state tax guide would focus on state-specific tax regulations, which differ from federal standards. Therefore, IRS Publication Circular E is the appropriate and authoritative source for federal tax compliance matters in the context of contracting and employment practices.