Tens of thousands of longshoremen went on strike at midnight ET, closing major ports along the East and Gulf coasts and choking supplies of everything from produce to auto parts.

Consumers are unlikely to feel the impact unless a strike lasts several weeks, as businesses and logistics companies have taken preventive measures to blunt the impact as the holiday shopping season is about to start. But a work stoppage could still cost the U.S. economy several hundred million dollars to $4.5 billion a day, analysts and business groups say. The costs resulting from diverting goods along longer routes would be passed on to consumers.

The ports handle about half of U.S. ocean imports. Varying estimates indicate the strike involves 25,000 to 50,000 members of the International Longshoremen’s Association. All told, the ILA has 85,000 members. Union leaders argue that major global freight forwarders have reaped huge profits since supply chain problems pushed up freight rates during the pandemic, and say workers have not sufficiently shared in those profits.

In a video posted to an ILA Instagram account, Harold J. Daggett addressed union workers at Maher Terminals in Elizabeth, New Jersey.

“This will go down in the history of what we do here,” he said.

“They can’t survive for too long,” he added.