Three employees at a large UPS facility in the greater Boston area have tested positive for the coronavirus and two dozen more have been quarantined on a doctor's orders, according to their union, Teamsters Local 25.

A UPS spokesperson would not confirm or deny the assertion, or answer questions about infected employees at any UPS location. The spokesperson told NBC News that the company is "not confirming employee cases for employee privacy reasons," and that information about any cases that need to be disclosed for public health reasons will come from government authorities. If an employee is diagnosed, the company follows guidance from the local department of health to clean and disinfect the area and communicate with people in the area that there was a diagnosis.

Sean O'Brien, the president of the Teamsters local, announced the cases at UPS' Chelmsford hub, located near Lowell, Massachusetts, in a letter sent Monday to members who work there.

O'Brien wrote he was informing members what the union knew about the COVID-19 cases in Chelmsford because UPS was "refusing to provide critical information to its employees regarding positive and presumptive positive COVID-19 cases in the facility."

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The union, which represents more than 12,000 workers in the Boston area, many of them employed by UPS, sent a previous letter to the company three days earlier, demanding it notify employees about what at the time was one positive case in the facility and 11 presumptive positive cases for quarantined employees. The first letter also demanded the company "immediately begin providing gloves, masks, hand sanitizer and Purell wipes to the employees daily."

In both letters, union officials said UPS had not done enough to prevent the virus from spreading throughout its facilities.

"In my opinion, the Company has made zero efforts to protect its employees," O'Brien wrote. "Teamsters Local 25 is actually appalled at the absolute lack of an appropriate response to the pandemic and incomprehensible refusal to provide equipment and products" such as gloves and sanitizer.

UPS strongly disputed the union's accusations. Spokesperson Matthew O'Connor told NBC News that O'Brien's statement is "simply not accurate, as we have undertaken extensive actions [to protect employees] ... We are actively communicating with employees about recommendations for protecting their health including personal hygiene, social distancing and other protocols. We are regularly urging employees to maintain social distances and not touch their face, and to wash their hands often and take other protective measures."

O'Connor noted that the company has increased "aircraft, vehicle and equipment cleaning processes" and modified parts of its business to increase social distancing, such as eliminating signature delivery.

The letter sent by the Teamsters to UPS on Friday laid out a list of issues, some that contradict O'Connor's statement. The letter said the company was not cleaning or sanitizing trucks, equipment and work areas on a daily basis; not providing instructions to employees on how to reduce the spread of the coronavirus; and refusing to inform members when a co-worker has been quarantined by a doctor with COVID-19 symptoms.

When UPS did not respond to the letter, the union informed members about the cases it knew of Monday, in a letter first reported by WCVB-TV of Boston. The numbers had gone up to three positive tests and more than two dozen quarantined with symptoms or because of family members who had tested positive. The union also provided workers with information on which parts of the 1,500-person facility the three positive workers had recently worked in.

The UPS spokesperson told NBC News that the company is "in regular contact with Mr. O'Brien and other local union leaders. The company has been, and will continue, to address their concerns."

These are not the first known cases among UPS workers, though there is no public data on the infection rate of delivery workers. On March 20, O'Connor confirmed to NBC San Diego that an employee in San Diego tested positive for COVID-19.

O'Brien promised to keep union members informed, and ended the letter by stating the union will "continue to pressure UPS to finally be honest with its employees and put people before packages and profits."