The head of the Teamsters Union says a third of a million workers at UPS will likely walk off the job on August 1, after slamming the shipping company’s proposed union contract as “appalling.” Teamsters President Sean M. O’Brien said in a statement, “The largest single-employer strike in American history now appears inevitable. Executives at UPS, some of whom get tens of millions of dollars a year, do not care about the hundreds of thousands of American workers who make this company run.” The Teamsters are demanding UPS exchange its last, best and final offer no later than Friday. Earlier this month, 97% of unionized UPS workers voted to authorize a nationwide strike if managers don’t agree to a new union contract by July 31.