Flyers threatening to “exterminate” certain Golden Gate Transit bus drivers were discovered in the agency’s buildings and have been reported to law enforcement, the Golden Gate Bridge district said Monday.

The flyers were posted at the San Rafael Transit Center and bus facility early Monday morning, the district said. The notes, signed by “The Pro Union Posse,” call on union members to place “agonizing discomfort and distress against” at least 10 drivers whom the flyer said refuse to pay dues to the bus operators’ union, Amalgamated Transit Union Local 1575.

“Union Tradition, when dealing with Freeloading Scabs, is to rid them from our midst, by any means necessary, e.g. Exterminate….. Exterminate ….. Exterminate,” the printed flyer states.

The note goes on to list examples such as “isolation, shunning, worries where they park vehicles or personal property, backpack, lunch etc. live in fear of the unexpected, always looking over shoulders,” the flyer reads.

Denis Mulligan, general manager of the Golden Gate Bridge, Highway and Transportation District, said the district was contacted by drivers Monday morning. He said it is investigating by examining video footage, checking employee badge access and interviewing employees to determine who posted the flyers. The incident also has been reported to the San Rafael Police Department, Mulligan said.

“We have a zero-tolerance policy of threatening violence within the workforce,” Mulligan said.

The notes come just months after the May 26 massacre at the Santa Clara Valley Transportation Agency bus center in San Jose in which an employee, Samuel James Cassidy, shot and killed nine of his coworkers before killing himself.

David Crockett, a Golden Gate Transit bus operator with the district for more than 10 years, was among the drivers listed on the flyers. He discovered one of the notes on the break room refrigerator on Monday morning.

Crockett said the incident has shaken him to the point that he says he no longer feels comfortable going to work.

“Now I’ve got to live in fear over this and looking over my back, looking at what’s next, who’s behind me,” Crockett said.

After reporting it to a dispatcher, Crockett asked to speak with the human resources department but was told no one was available. A district staff member eventually contacted him, took his information and told him they would contact him again, he said. Crockett said he had yet to hear from anyone as of Monday afternoon.

“It’s leaving me in the dark with threats against me and coworkers that I work with,” Crockett said.

Amalgamated Transit Union Local 1575 president Shane Weinstein condemned the threats and said he has contacted union members about the incident

“We would never endorse this, condone this, do anything,” Weinstein said. “It’s kind of jarring.”