This publication explains your tax responsibilities as an employer.
2020 Percentage Method Tables for Automated Payroll Systems -- 26-NOV-2019
Other Items You May Find Useful
About Publication 15-A, Employer's Supplemental Tax Guide (Supplement to Circular E, Employer's Tax Guide, Publication 15)
About Publication 80, Circular SS - Federal Tax Guide for Employers in the U.S. Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands