Final answer:
The FASB prefers that unrecognized prior service cost be amortized using the straight-line method, evenly distributing the cost over the service periods of the employees benefiting from the pension plan amendment.
Step-by-step explanation:
The Financial Accounting Standards Board (FASB) sets standards for financial reporting and accounting, and one aspect they cover is the treatment of unrecognized prior service cost. This cost arises when a company amends its pension plan, resulting in an increase in projected benefit obligation. The preferred method for amortizing unrecognized prior service cost, according to FASB, is the straight-line method. This method evenly spreads the cost over the service periods of the employees who are expected to benefit from the plan amendment.