London (CNN Business)Seafarers, truck drivers and airline workers have endured quarantines, travel restrictions and complex Covid-19 vaccination and testing requirements to keep stretched supply chains moving during the pandemic. But many are now reaching their breaking point, posing yet another threat to the badly tangled network of ports, container vessels and trucking companies that moves goods around the world. In an open letter Wednesday to heads of state attending the United Nations General Assembly, the International Chamber of Shipping (ICS) and other industry groups warned of a "global transport system collapse" if governments do not restore freedom of movement to...