The Pension Benefit Guaranty Corporation guarantees payment of nonforfeitable pension benefits in covered, private-sector-defined benefit pension plans. Title IV of the Employee Retirement Income Security Act of 1974 (29 U.S.C. 1301 et seq.) provides for coverage of most private-sectordefined benefit pension plans that provide a benefit based on factors such as age, years of service, and average or highest salary. The Corporation administers two benefit insurance programs separately covering singleemployer and multi-employer plans. Nearly 40 million workers participate in more than 112,000 covered plans. Single-Employer Insurance: Under the single-employer program, the Corporation guarantees payment of a covered plan's basic benefits if that plan terminates without sufficient assets to pay those guaranteed benefits. Multi-employer Insurance: Under Title IV of the Act, as originally enacted, the Corporation guaranteed nonforfeitable benefits for multi-employer plans in a similar fashion as for single-employer plans. However, the payment of guaranteed benefits was at the agency's discretion under the provisions of the law that remained in force until August 1, 1980. The Multi-employer Pension Plan Amendments Act of 1980 (29 U.S.C. 1001) revised the law applicable to multi-employer pension plans by changing the insurable event from plan termination to plan insolvency. In accordance with the Act, the Corporation provides financial assistance to plans that are unable to pay basic benefits. The plans are obligated to repay such assistance. The act also made employers withdrawing from a plan liable to the plan for a portion of its unfunded vested benefits. Premium Collections: All defined benefit pension plans covered by Title IV of Employee Retirement Income Security Act are required to pay premiums under prescribed rates to the Corporation.