Metro-North Railroad said train service was temporarily suspended through Fairfield while authorities investigated a suspicious package near the station.
Metro-North spokesman Aaron Donovan said the suspension started at about 6:15 am on Friday in both directions. Trains were stopped before they got to the Fairfield station area.
Residual delays were expected.
Metro-North serves 281,000 riders a day in New York and Connecticut and is the nation's second busiest commuter railroad.