the PPA amends both the ERISA and Code. Different rules apply with respect to employer contributions made before 2007. Employee contributions are always 100% vested. Accrued benefits under a defined benefit plan must become vested at 100% after five years or under a 3rd-7th year gradual vesting schedule (20% per year beginning with the third year of vesting service, and 100% after seven years). (ref. 26 U.S.C. 411(a)(1)(B), 29 U.S.C. 203(a)(2).) Pension funding ERISA established minimum funding requirements for pension plans, which includes defined benefit plans and money purchase plans but not profit sharing or stock bonus plans. Before the Pension Protection Act of 2006 (PPA), a defined benefit plan maintained a funding standard account, which was charged annually for the cost of benefits earned during the year and credited for employer contributions. Increases in the plan's liabilities due to benefit improvements, changes in actuarial assumptions, and any other reasons were amortized and charged to the account; decreases in the plan's liabilities were amortized and credited to the account. Every year, the employer was required to contribute the amount necessary to keep the funding standard account from falling below $0 at year-end. In 2008, when the PPA funding rules went into effect, single-employer pension plans no longer maintain funding standard accounts. The funding requirement under PPA is simply that a plan must stay fully funded (that is, its assets must equal or exceed its liabilities). If a plan is fully funded, the minimum required contribution is the cost of benefits earned during the year. If a plan is not fully funded, the contribution also includes the amount necessary to amortize over seven years the difference between its liabilities and its assets. Stricter rules apply to severely underfunded plans (called "at-risk status"). The PPA has different funding requirements for multiemployer pension plans, which preserve most of the pre-PPA funding rules, including the funding standard account. Under PPA, increases and decreases in the plan's liabilities are amortized, but the amortization period for benefit improvements adopted after 2007 are shortened. As with single-employer plans, multiemployer pension plans that are significantly underfunded are subject to restrictions. The restrictions, which may limit the plan's ability to improve benefits or require the plan to reduce employees' benefits, vary depending whether a pension plan's funding status is termed "endangered", "seriously endangered", or "critical". The restrictions accompanying each deficient funding status are progressively more severe as funding status