A surprise and unauthorized school bus drivers strike impacted at least half of the city's student population this morning, according to the Boston Public School department. The work action, which BPS officials have condemned as "illegal", involves around 300 drivers and will impact about half of the city's 33,000 students who ride buses daily to public, parochial and charter schools.

The school department claims that the dispute centers on changes made by Veolia Transportation, a new bus contractor hired over the summer.

The city's interim schools superintendent John McDonough slammed the bus drivers union for the action, calling it "an unacceptable attempt to shut down our entire school system because the Union is unhappy with efforts to increase safety and improve on-time service."

Both mayoral candidates— John Connolly and Marty Walsh— have issued statements this morning condemning the strike and calling on drivers to return to work immediately.

The United Steelworkers (USW) released a statement from its District 4 Director John Shinn calling for the action to end and for all members of the Local 8751 to "resume work as soon as possible."

"This activity does not represent the majority of our members, who believe that our issues with Veolia Transportation must be addressed through proper avenues including our contractual grievance procedure and the National Labor Relations Board," Shinn said in a statement.

Schools remain open, but students will not be marked late and absences will be marked as "excused," the BPS says. There will be no afternoon activities in the BPS. Families can call 617-635-9520 for transportation info and the Mayor’s 24-Hour-Hotline is available at 617-635-4500.