“Both sides can be right,” said James Lightbourn, a former ship broker with experience managing hundreds of vessels who writes about maritime issues. He said the Jones Act waiver does undermine the long-term viability of domestic businesses while giving shippers cheaper options.

“This is the first time you’ve really seen sort of a chink in its armor,” he said of the law and the escalating battle for public support. “That, I think, has got a lot of folks sort of up in arms.”