A UAW member walking a picket line outside the Flint Assembly Plant on Thursday was "clipped" with a car mirror as a driver approaching the plant tried to cross the strike line. The driver then climbed out of the car and punched the striking worker, a person briefed on the investigation told the Free Press.

Detective Sgt. Tyrone Booth, spokesman for the Flint Police Department, said, "We are investigating a complaint where someone was allegedly assaulted. We cannot go into the details because it's an ongoing investigation." No charges had been filed.

The driver, reportedly not employed by GM, was going to the plant, the person briefed by police said, for a job application for a nonunion trucking company that does work for the automaker.

"Police described the situation in great detail," said the source briefed on union safety at the Flint plants. "So the gentleman stopped and got out and said, 'I'm here to fill out a f**ing application for Precision trucking and he walked up and hauled off and punched the guy."

UAW Local 598 President Ryan Buchalski, who represents about 5,000 workers at Flint Assembly, couldn't be reached Friday for comment.

Details involving the UAW worker, his member union and the status of the investigation were not immediately available.

Asked to describe the relationship between GM and Precision, GM spokesman Jim Cain said, "We work with both union and nonunion shippers. We are not commenting on our relationship with any of our freight and logistics suppliers."

He added: "We have freight companies attempting to move vehicles, components and parts in and out of facilities," Cain said. "We are not going to confirm the names of these suppliers or what they may be moving. I can tell you we are not removing equipment out of plants."

The Teamsters union announced early this week that its truckers would not cross the UAW picket line and, therefore, not pick up or deliver vehicles or supplies.

Cain said GM people moving vehicles at plants are not hourly workers or Teamsters. "They are salaried. Also, there are vehicles shipping from offsite storage lots where there are not picket lines."

Union officials are working with law enforcement to track threats and monitor behavior of union and nonunion people involved as the national strike affecting 46,000 GM employees. Police have been monitoring sites.

"Safety is our first priority and people who have concerns about crossing picket lines are not required to do so," Cain said Friday.

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A man at Precision Industries in Flint, which is not a trucking company, said he wished people would stop contacting his firm, a manufacturer of plastic injection and structural foam injection molds and molded plastic parts for more than 50 years.

Tensions are high at several strike sites.

At GM's assembly plant in Spring Hill, Tennessee, on Wednesday, Maury County sheriff's deputies arrested nine protesters when they refused to stop blocking the south entrance to the plant. A 10th arrest came when someone drove recklessly through plant's entrance, sheriff's officials said.

News reports said the picketers had been asked by law enforcement to move when they blocked an entrance to the plant. Herron said, "They weren't aggressive; they were just going ahead and making a point."

Plant officials told about 400 salaried workers assigned to Spring Hill to work from home following the arrests.

On Friday, union officials denied employee reports of nails on the road that were confirmed by General Motors representatives.

But, said UAW Spring Hill Local 1853 Bargaining Chairman Mike Herron, "We've got no confirmation of any nails. I've been out there every day and I don't know where that narrative is coming from. We certainly do not condone that."

Contact Phoebe Wall Howard: 313-222-6512 orphoward@freepress.com.Follow her on Twitter@phoebesaid. Read more on Ford and sign up for our autos newsletter. The Tennessean of Nashville contributed to this report.