The National Retail Federation also warned the negative growth will accelerate, with imports through the summer expected to be at least 20% lower than the corresponding month last year.
Trade disputes cast a pall over US manufacturing and trucking as exports and imports drop, PMI surveys show.
There remains no guarantee of safety for ships, crew and cargo passing through the waterway, which means it would likely be out of bounds for the rest of the year, says CEO Vincent Clerc.