According to the lawsuit, Mendoza, 41, was savagely beaten by Police Sergeant Thomas O'Grady. O'Grady was riding his bike on the left of the bus, Mendoza said, when he cut in front of the bus.
According to Mendoza's attorneys, O'Grady accused Mendoza of cutting him off and came aboard the bus to beat him near State and Monroe.
"We feel the attack against Mr. .Mendoza was brutal violent and a violation of his civil rights," said Darrell Jefferson, ATU Local 241.
Mendoza, who did not talk about the incident, let his union and lawyer speak for him when announcing the lawsuit on Thursday. The lawsuit was filed against Police Sergeant Thomas O'Grady and the City of Chicago. His attorney hopes CTA videotape will help the case.
The video that was released on Thursday shows two uniformed officers boarding the bus and sitting in the back. Next, his attorney claims O'Grady is shown dropping his bike outside of the bus door, then boarding the bus. The rest isn't captured on tape, but Mendoza's attorney said O'Grady beat the bus driver, got off the bus, and then got back on.
"He came back towards Mr. Mendoza again all the while Mendoza was still in his seat," said Michael Simmons, ATU Local 241.
As seen on the tape, the uniformed officers on the bus intervened and took the off-duty police sergeant off the bus. Mendoza was taken to the hospital for his injuries.
O'Grady has not been charged with a crime. Mendoza's union wants the sergeant fired.
"we urge Mayor Daley and Supt. Jody Weis to step in take action against the wrongful violent behavior of the officer," said Jefferson.
Mendoza is suing the city for more than $1 million.
The Cook County state's attorney is investigating the incident. A spokesperson says it will take time because of the difficulty in finding witnesses. The CTA and the Independent Police Review Authority are investigating as well.