Sept 4 (Reuters) -

About half of the workforce at Marathon Petroleum's ( MPC )

Detroit refinery will begin striking on Wednesday, following

months of unsuccessful negotiations over pay and safety

concerns, the Teamsters union said.

The union has been negotiating with Marathon, the country's

largest refiner by volume, for the past nine months, demanding

better pay and improved work schedules.

Marathon said it does not expect the strike to impact

operations at the facility.

"We are fully prepared and have implemented plans to

continue safely operating the facility," the company said in a

statement.

Marathon's Detroit refinery has a crude oil refining

capacity of 140,000 barrels per day, processing sweet and heavy

sour crude oils into products such as gasoline and distillates.

It employs about 273 Teamsters members, 95% of whom

authorised the strike, the union said.

The refinery has about 525 employees, including both union

and non-union workers.