Dockworkers at ports across a major swathe of the US coastline are signalling that they could strike, raising the spectre of supply-chain constraints in the container sector when the existing contract ends on 30 September.

Concerns are mounting after the International Longshoremen’s Association (ILA), the labour union that represents dockworkers at container ports across the Atlantic Seaboard and Gulf Coast, pulled out of negotiations with employers on 10 June — the day the talks were set to begin.