Pension Benefits Protection Act of 2005

Pension Benefits Protection Act of 2005 - Amends the Employee Retirement Income Security Act of 1974 (ERISA) and the Internal Revenue Code with respect to pension benefits of employees in defined benefit plans.

Directs the Secretary of the Treasury to apply Code provisions regarding continued accrual of benefits beyond normal retirement age under a defined benefit plan, which prohibit certain discrimination based on age, without regard to the portion of the preamble to a specified Treasury Decision which relates to allocation of interest adjustments through normal retirement age under a cash balance plan.

Prohibits forced conversions of certain defined benefit plan participants to cash balance plans, and other such plans that are hybrids of defined benefit and defined contribution plans, by plan amendments which: (1) change the way the accrued benefits to participants or beneficiaries are expressed; and (2) reduce the rate of future benefit accrual of one or more participants. Requires employers, at the time such amendment takes effect, to provide employees who have attained 40 years of age or 10 years of service with certain notices and an election upon retirement to receive benefits as determined either under the plan in effect at time of retirement or under the plan in effect immediately before the plan amendment.

Sets forth a formula to determine when a plan amendment adopted by a large (100 or more participants) defined benefit plan shall be treated as wearing away accrued benefits.