A PSS lands as a carrier rate announcement scoped to a trade lane, with an effective date, per-container levels that differ from lane to lane, and often no stated end date; despite the name, carriers have also applied PSS-labelled charges during disruptions, not only in calendar-season peaks. The desk has to catch the announcement before it takes effect, work out which open quotes and bookings fall inside its scope, and decide whether a filed service contract shields the shipment or the customer must be re-quoted; on trades covered by the US Shipping Act, a surcharge binds the carrier only if it sits in the published tariff or a service contract filed with the Federal Maritime Commission. The term to keep separate is the GRI (general rate increase), which moves the base freight rate itself, while a PSS is a separate, temporary surcharge applied on top of that base rate.
Glossary
PSS (Peak Season Surcharge)
A temporary surcharge a carrier applies on top of base ocean freight during high-demand periods, announced per trade lane with an effective date.