Section 100121 of P.L. 112-141 , the Moving Ahead for Progress in the 21 st Century Act (MAP-21, enacted July 6, 2012) provides the authority for a new phased retirement option for certain employees covered by the Civil Service Retirement System (CSRS) or the Federal Employees' Retirement System (FERS), the retirement plans that cover most of the civilian federal workforce. Under phased retirement, an eligible federal employee may work a reduced-hour schedule and simultaneously receive a prorated federal retirement benefit (or annuity ) under CSRS or FERS. For eligible federal employees, phased retirement is a voluntary option that requires approval from their employing federal agencies. Employees participating in phased retirement generally must also engage in mentoring activities (except for U.S. Postal Service employees). According to the Office of Personnel Management (OPM), which administers phased retirement, "The main purpose of phased retirement is to enhance the mentoring and training of the employees who will be filling the positions or taking on the duties of more experienced retiring employees." Phased retirement allows certain federal employees who are otherwise eligible for retirement under CSRS or FERS to work a reduced schedule while receiving a reduced salary as well as a prorated percentage of their retirement benefits. Before P.L. 112-141 , federal law generally prohibited the concurrent receipt of a federal salary and a federal pension (i.e., dual compensation ). Prior to the enactment of phased retirement, the situation of dual compensation arose in the context of current federal retirees who returned to work in federal service (i.e., reemployed annuitants ). Over the past several decades, Congress has provided authority for waivers in some circumstances to the general reduction in pay usually required for dual compensation. These waivers accomplish several policy goals, including hiring for highly skilled or difficult-to-fill positions. Individuals receiving retirement benefits under CSRS or FERS may be reemployed by the federal government in some situations. These individuals may not simultaneously collect a federal civil service retirement benefit and a salary for current employment with the federal government in most circumstances. Reemployed annuitants generally have their federal salaries reduced by the amount of their CSRS or FERS retirement benefits while they are reemployed. Before 1990, there were no exceptions to the prohibition on concurrent receipt of a federal salary and a federal retirement annuity. Since 1990, several types of waiver authority have been provided to allow certain reemployed annuitants to receive their full salaries and full CSRS or FERS retirement benefits. First, the Federal Employees Pay Comparability Act of 1990 ( P.L. 101-509 ) delegated authority to the Director of OPM to waive the prohibition on dual compensation in certain exceptional circumstances and allow a reemployed annuitant to receive both a federal salary and a federal retirement annuity concurrently. Under the 1990 law, the head of an executive branch agency may request that OPM temporarily waive the prohibition on dual compensation on a case-by-case basis for employees in positions for which there is exceptional difficulty in recruiting or retaining qualified employees. If a federal annuitant is reemployed under a waiver that allows concurrent receipt of a federal annuity and a federal salary, he or she accrues no new retirement benefits under CSRS or FERS. Second, the National Defense Authorization Act for Fiscal Year 2004 ( P.L. 108-136 ) delegated to the Secretary of Defense authority to hire federal annuitants without reducing their salaries by the amount of their annuities. The approval of the Director of OPM is not required. Under this law, a federal annuitant hired by the Department of Defense is entitled to receive both a federal annuity and the full salary for the position into which he or she is hired. The reemployed annuitant does not accrue additional CSRS or FERS retirement benefits during the period of reemployment. Finally, the National Defense Authorization Act for Fiscal Year 2010 ( P.L. 111-84 ) allowed the head of a federal agency to appoint an individual who is receiving an annuity under CSRS or FERS to a temporary, part-time position in civilian federal employment without the offset to salary otherwise required by law. Employment under this authority is limited to 520 hours of service performed in the 6 months after the date on which the annuity begins; 1,040 hours of service performed in any 12-month period; and 3,120 hours of service performed over the individual's lifetime. The total number of individuals appointed by the head of an agency under this authority may not exceed 2.5% of the total number of full-time employees of the agency. If the total number of appointments exceeds 1% of the number of an agency's full-time employees, the agency must submit to Congress a report explaining why the number of appointments exceeds this threshold. The waiver authority granted under P.L. 111-84 is scheduled to expire on October 27, 2014. Except for cases in which a dual compensation waiver has been granted by the Director of OPM, the Secretary of Defense, or an agency head, a reemployed annuitant's retirement annuity continues during the period of reemployment, and his or her pay is reduced by the amount of the annuity. Reemployed annuitants earn additional retirement benefits while reemployed, unless hired under a waiver granting simultaneous receipt of salary and pension. If the period of reemployment lasts one year or more, the individual is eligible for a supplemental annuity when he or she retires. If the period of reemployment lasts five years or more, the individual can elect a redetermined annuity. Section 100121 of P.L. 112-141 created a phased retirement authority under 5 U.S.C. §8336a (CSRS) and 5 U.S.C. §8412a (FERS). Phased retirement provides a new personnel option for certain retirement-eligible federal employees covered by CSRS or FERS to work a reduced schedule while receiving a reduced salary as well as a reduced percentage of their CSRS or FERS retirement benefits. Phased retirees, except for phased retirees employed at the U.S. Postal Service, are subject to a requirement that they spend at least 20% of their reduced work hours engaged in mentoring activities. Unlike existing waivers for dual compensation in the situation of reemployed annuitants, phased retirement is designed as a human resources instrument to allow eligible employees to reduce their work hours before they separate from federal service and make up for the reduced salary through receipt of prorated retirement benefits. Phased retirement also provides agencies with another tool to transfer knowledge to newer employees through mentoring. As explained in OPM's final rule for phased retirement, published on August 8, 2014: Phased retirement is designed to assist agencies with knowledge management and continuity of operations in the short term.... Phased retirement is simply another tool to enable agencies to manage their workforce, promote best practices, and encourage experienced employees to spend some time mentoring the next generation of experts. The statutory language for the phased retirement authority sets out a 50% reduced work schedule for participants. Therefore, if an individual's full-time schedule is generally 40 hours per week and 80 hours per pay period, then the reduced work schedule under phased retirement would be generally 20 hours per week and 40 hours per pay period. As a result of the 50% reduced work schedule, individuals receive 50% of their previous salaries when they enter phased retirement. The authorizing law also provides OPM with the authority to offer additional working percentage options for phased retirees of anywhere between 20% and 80%. Under current regulation, however, only the 50% reduced work schedule will be available initially to phased retirees. OPM justifies the present, limited structure of phased retirement work schedules as a consequence of the complexity of implementing this new human resources option. While an employee is in phased retirement, the reduced work schedule may not be changed. Retirement-eligible employees may not make more than one phased retirement election during their lifetimes. Phased retirees may not be employed in more than one position at a time; although they may transfer positions within or across agencies only if the transfer does not result in a change in the reduced work hours. Phased retirement may be either open-ended in status or subject to a time limit that is mutually agreed upon by the employing agency and the eligible employee. Agencies have discretion with regard to whether to establish time limits for phased retirement. Phased retirees may submit an application for full retirement at any time. Phased retirees may also request to return to regular employment, which their employing agency must approve. (If the agency does not approve this request, the employee may continue as a phased retiree or enter full retirement.) Entry into phased retirement is voluntary for an eligible employee. Phased retirement is not an entitlement; it requires the mutual agreement of the eligible employee and the employee's agency. Federal agencies have the discretion to determine whether to implement phased retirement. Under the implementing regulations, agencies may begin accepting applications from employees for phased retirement beginning November 6, 2014. Eligible employees must secure written approval from the employing agency to enter into phased retirement. Agencies must have written criteria in place that will be used to approve or deny applications for phased retirement. OPM has stated that agency's written criteria may include, but should not be limited to, the following: "Criteria that will be considered when approving requests; Designation of officials with authority to approve requests; Use of time limits as a condition of approval of requests; Positions or geographic locations that may be included or excluded; and Process for handling multiple requests when the agency is unable to approve all requests received."