This document contains a final regulation that establishes a safe harbor period during which amounts that an employer has received from employees or withheld from wages for contribution to certain employee benefit plans will not constitute "plan assets" for purposes of Title I of the Employee Retirement Income Security Act of 1974, as amended (ERISA), and the related prohibited transaction provisions of the Internal Revenue Code. This regulation will enhance the clarity and certainty for many employers as to when participant contributions will be treated as contributed in a timely manner to employee benefit plans. This final regulation will affect the sponsors and fiduciaries of contributory group welfare and pension plans covered by ERISA, including 401(k) plans, as well as the participants and beneficiaries covered by such plans and recordkeepers, and other service providers to such plans.