The move allowed Amalgamated Transit Union Local 26 President Fred Westbrook to distance the union from the decision to close down services despite a union rally scheduled downtown to focus on recent attacks on city bus drivers.
Westbrook said Detroit chief compliance officer Gary Brown had informed him 156 of 400 bus drivers had called in sick. He also said the union "never said we were calling off sick."
"The department made that decision," Westbrook said.
The Detroit News reported Monday a union rally scheduled for Monday downtown was expected to focus on recent events in which passengers had threatened or attacked drivers.
Westbrook said in the past week two drivers were stabbed and one threatened by three passengers. Another had urine thrown at her, the newspaper said.
"We are going beyond the duty required of us. I want to let [passengers] know it's not our fault," Westbrook said.
The News said a shortage of buses in the financially struggling city had resulted in longer waits at bus stops and overcrowded buses, sparking anger among passengers.
"The deterioration of the bus system is not the drivers' fault," Westbrook said.