Chris Zimmerman, chairman of the Arlington County Board, called on its transit contractor, Forsythe Transportation, and the bus drivers’ union, the American Federation of State, County and Municipal Employees Local 3001, to come to an agreement immediately.

In a statement Wednesday, Zimmerman called the situation that has led to a driver walk-out and multiple delays on Arlington Transit’s 13 bus routes since Monday “simply unacceptable.”

“It is critical to move expeditiously to resolve these issues and restore bus service at normal levels,” Zimmerman said. “We call for an immediate agreement between management and labor that will provide for the prompt restoration of service and an impartial investigation of workers’ concerns and a fair mediation of the matters in dispute.”

The county has no authority to intervene in a labor dispute between one of its contractors and its employees.

“Drivers have expressed concerns that need to be taken seriously, including allegations of sexual harassment and the improper disciplining of a union representative,” Zimmerman said.

About 9,000 people use ART buses each day, totaling more than 2 million a year.