Some warehouse workers said supervisors had rebuffed them when they pleaded for bleach, masks, gloves and a ready supply of hand sanitizer. In some facilities, even hand soap and paper towels are scarce, employees said. Employees continue to be jammed shoulder to shoulder along conveyor belts and required to maintain rituals such as security pat-downs.

Many workers in the logistics and delivery industry get at most a handful of paid sick days a year. That can push them to work through coughs and fevers. Now, with so many people and businesses relying on a functioning delivery system, the pressure to go in has only intensified, workers said.

A package sorter in a UPS facility near San Francisco said she had been going into work every day, even though her “throat feels like broken glass.” The worker, who requested anonymity, said she was petrified that she would lose her job if she called in sick. “I can’t afford to be homeless,” she said.

Another UPS package handler, Jeff Donigian, who works in Manchester, N.H., said he had been showing up to work feeling ill and coughing. He told a supervisor; he was told to go in anyway.