A North Carolina woman who was a U.S. Postal Service worker was found unresponsive in a bathroom shortly after working in the back of a postal truck without air conditioning on a sweltering day, her family says.

Wednesday "Wendy" Johnson, 51, died on June 6 after she "dedicated over 20 years to the United States Postal Service," according to her obituary on the Knotts Funeral Home's website.

Her son, DeAndre Johnson, told USA TODAY on Monday that his sister called to tell him their mother had passed out while he was working in Fayetteville, North Carolina. She called him back five minutes later to tell him their mother had died.

"I was on my way to Maryland," said Johnson, a 33-year-old truck driver. "It really didn't hit me until I pulled over."

'It must have been so hot'

Johnson recalled his mother telling him during previous conversations that it was hot in the back of the U.S.P.S trucks. He then questioned his mother, who was a supervisor at her post office location, about why she was working in the back of trucks.

"It must have been so hot," he said about the day his mother died. "It was 95 degrees that day, so (she was) in the back of one of those metal trucks with no A/C."

Sa'ni Johnson, Wendy Johnson's daughter, told WRAL-TV that as soon as her mother got back from getting off the truck she went to the bathroom. When somebody came to the bathroom 15 minutes later, they found her unresponsive, she told the Raleigh, North Carolina-based TV station.

Based on conversations with family members who work in the medical field, DeAndre Johnson said they believe his mother died of a heat stroke. USA TODAY contacted the North Carolina Chief Medical Examiner on Monday and is awaiting a response regarding Johnson's cause of death.

OSHA investigating Wednesday Johnson's death

The Occupational Safety and Health Administration (OSHA) is investigating Johnson's death as heat-related, DeAndre Johnson said.

"My mother died on the clock," he said. "She worked for a government job and she died on government property."

In response to Johnson's death, U.S.P.S. leadership sent her family a name plaque and held a memorial service in her honor, her son said. While the gestures were welcomed, DeAndre Johnson said he believes the agency was "saving face."

USA TODAY contacted U.S.P.S., and an agency spokesperson said they were working on a response.

DeAndre Johnson remembers his mother as 'kind' and 'caring'

Sa'ni Johnson said she considered her mom her "community" because she "didn't need nobody else but her," WRAL-TV reported.

DeAndre Johnson said he hopes his mother's death will bring awareness to workplace conditions at the postal service, particularly inside its trucks. He said he'll remember his mom, a native of Brooklyn, New York, as someone who was kind and caring but certainly no pushover.

"You can tell the Brooklyn was still in her," he said.