Social Security Act
Section 18. Employee's Contributions. - Beginning on the last day of the calendar month when an employee's compulsory coverage takes effect and every month thereafter during his employment, the employer shall deduct and withhold from such employee's monthly salary, wage, compensation or earnings, the employee's contribution in an amount corresponding to his salary, wage, compensation or earnings during the month in accordance with the monthly salary credits, the schedule and the rate of contributions as may be determined and fixed by the Commission, subject to the provisions of Section 4(a)(9) of this Act.
The monthly salary credits, the schedule and the rate of contributions shall also apply to self-employed, voluntary, and other members.