Call it the overweight-container conundrum.

Last Thursday, the U.S. Coast Guard held an extraordinary listening session to discuss its role in enforcing an amendment to a 102-year-old international treaty requiring shippers to certify in writing the accurate "verified gross mass" of a container, which includes the cargo and equipment, for the box to be loaded. According to those attending the session, Rear Adm. Paul Thomas said the Coast Guard's jurisdiction extends only to activity aboard ships, and that the agency has no plans to change its enforcement procedures when the amendment takes effect July 1.

The Agriculture Transportation Coalition, which represents U.S. agricultural and forest-products exporters and which opposes the amendment, interpreted Thomas' remarks as meaning the Coast Guard will focus enforcement on container lines and terminal operators, not shippers. However, the World Shipping Council (WSC), which represents virtually every global container line, said the admiral's comments only affirmed the Coast Guard's mission to provide enforcement aboard the vessel, and that they change nothing as far as the amendment is concerned.

Regardless of interpretation, shippers worldwide must still confront the language—which is contained in the 102-year-old Safety of Life at Sea (SOLAS) treaty and has the force of law in 171 member countries—that puts the onus on them to submit an accurate read of a container's "gross mass." Without that verification, the box will not be loaded. The amendment was adopted amid concerns that illegally overweight containers could contribute to a seagoing incident where a vessel could be sunk or damaged.

Peter Friedmann, executive director of the U.S. exporter group, said it would continue to work with all stakeholders to ensure compliance with the language. He added, however, that the carriers must determine what form of shipper documentation will be acceptable to them, especially since it was the WSC that lobbied for the amendment in the first place. For example, Friedmann suggested carriers consider accepting a shipper's written statement that the weight of the cargo and dunnage—material used to load and secure cargo during transit—does not exceed the container's capacity.

The exporter group has said it would be difficult, if not impossible, for shippers to certify the gross mass of a container because they don't own or control the equipment. Shippers should be responsible only for certifying the weight of the cargoes they tender, the group said.

Carriers may also want to lobby their respective governments to convince the International Maritime Organization (IMO), which oversees the treaty, to amend the provision's language, Friedmann added. Separately, the coalition has asked the U.S. government to delay the amendment's implementation until the U.S.' top 15 trading partners are on board with it.

Exporters are unlikely to find a sympathetic ear from U.S. ports. Curtis Foltz, the outgoing head of the Georgia Ports Authority, which owns and operates the containerport of Savannah and the bulk and breakbulk Port of Brunswick, said in a phone interview last week that shippers bear full responsibility for verifying a box's gross weight, and scoffed at the notion that shippers can't provide accurate information because they don't control the container. Lee Peterson, a spokesman for the Port of Long Beach, said in an e-mail that while the port community is awaiting Coast Guard guidelines, "it will be up to the shippers to comply, and up to the Coast Guard to enforce." The port will work with its tenant terminal operators to determine the impact on operations, Peterson said.

Joe Harris, a spokesman for the Port of Virginia—which like the GPA and the ports of Charleston and Houston, owns and operate its facilities—said Virginia will be ready for the July 1 compliance deadline. Harris declined to elaborate.