A Black mechanic for the company that provides school bus services for the St. Louis school district said he found a noose at his workstation, leading at least 100 drivers to stop work in a show of support.

The work stoppage began Monday and continued Tuesday for St. Louis drivers employed by Missouri Central School Bus. Most after-school activities in St. Louis Public Schools were called off both days. And about 40 bus routes were uncovered Tuesday morning, forcing parents to make other plans.

“We, like you, are very much caught in the middle of this ugly dispute at Missouri Central,” a statement from the school district said.

Mechanic Amin Mitchell said he found a noose last week at his workstation. Mitchell told the St. Louis Post-Dispatch that he believed the noose was meant to send a racist message to intimidate him after an argument with a manager over Mitchell’s concern that some bus brakes were inadequate.

Mitchell posted social media video of the noose, fashioned from a thin rope and lying on the floor in the area where he works.

A St.Louis school bus mechanic found a noose at his workstation, and colleagues across the district are joining him in protest. School bus service has been disrupted across the city. (Fox News)

“That’s a message that says, ‘If you don’t stop doing what you’re doing, something bad is going to happen right away,’” Mitchell told the newspaper. He didn’t immediately return messages from The Associated Press seeking comment.

Missouri Central said in a statement that it will hire an independent third party to investigate claims by Mitchell and others of racism.

“At Missouri Central, our policy is to provide and foster a work environment that is welcoming to all regardless of age, race, ethnicity and sexual orientation,” the statement said. “There is zero tolerance for any behavior that violates this policy.”

The state, city and county NAACP chapters called Tuesday for a federal or state investigation.

The drivers are members of Laborers’ International Union of North America. Because their contract does not permit strikes, drivers told the Post-Dispatch, they called in sick with “personal issues.”