UPS has agreed to mandate air conditioning in its delivery fleet as part of ongoing negotiations with workers in the Teamsters union. A number of UPS delivery drivers have become sick from working in extreme temperatures. Last summer, a 24 year-old UPS driver in Southern California died on the job, which his family said was caused by the heat. This comes as some 330,000 union members are voting to authorize a possible August strike against UPS, in what would be the largest single-employer strike in U.S. history.