Longshoremen’s union says wage demands must be met or members will strike on Tuesday for first time since 1977

Ten of the busiest ports in North America are at risk of shutdown next week, as a leading union warns that 45,000 workers stand ready to walk off the job if industry operators fail to make key concessions.

The International Longshoremen’s Association (ILA) has accused the United States Maritime Alliance (USMX), which represents 40 ocean carrier and terminal operators, of making “insulting offers” to staff demanding higher pay and commitments on automation.

Workers are slated to strike on Tuesday if a new agreement is not reached, hitting 36 ports along the east and Gulf coasts of the US in what would be the first work stoppage since 1977.

JP Morgan analysts have estimated a strike could cost the US economy $5bn per day. A one-day strike backlog could take an estimated four to six days to clear, according to analysts at Sea-Intelligence, a shipping advisory firm.