A Texas UPS driver fell ill while working during a scorching heat wave and later died.

According to a statement from UPS, Christopher Begley, 57, died this week shortly after becoming sick earlier this month while on his route in North Texas, where the high temperature at the time topped 100 degrees. The exact cause of death has yet to be determined, and authorities are investigating,

“We train our people to recognize the symptoms of heat stress, and we respond immediately to any request for help,” the delivery giant told CBS MoneyWatch. “We are cooperating with the authorities as they continue to investigate the cause of death.”

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The death comes roughly a month after UPS struck an agreement with the Teamsters Union that would require the company to install air conditioning in its delivery vans, among other improvements to drivers’ working conditions.

Begley, who worked at UPS for 27 years, first told managers that he was feeling sick on August 23 and was removed from service that same day, according to UPS. Begley later requested and received several days off from work, the company added. 

UPS “immediately responded” to the driver’s call and “made sure he had water and was resting in a cool environment,” the company said. Begley denied medical assistance “multiple times” after falling ill, telling the company he had recovered, according to UPS.

UPS managers found out several days later that Begley was in the hospital, where he died shortly afterward, the package carrier said in its statement. 

Installing AC units in UPS’ delivery trucks was a major issue for union members as they threatened to strike this summer before ratifying a new contract on August 22.

Last year, photos taken by UPS drivers showed thermometers in the company’s trucks were reading temperatures of up to roughly 120 degrees Fahrenheit, according to a post from a Teamsters group on X (formerly known as Twitter). Last summer, a video of a UPS driver collapsing from apparent heat exhaustion also sparked public outrage.