Marathon Petroleum Corporation (MPC) shares are down in premarket trading after half of its Detroit refinery workforce went on strike over unresolved pay and safety concerns. The union has been negotiating with Marathon for nine months, seeking improved pay and work schedules. The refinery, with a capacity of 140,000 barrels per day, processes both sweet and heavy sour crude oils into gasoline and distillates. Despite the strike, Marathon has stated its preparedness to continue operations safely. Despite this news, Marathon recently reported strong second-quarter results, including revenue exceeding estimates and an adjusted EPS surpassing the consensus.