The warning came shortly after train doors became stuck at both Parliament and Lyon stations, causing system-wide delays that lasted about 90 minutes. A similar incident messed up Tuesday's morning commute.
"There needs to be some punitive measures, and people have to understand that when the doors are about to close, you don't pry them back open," Watson told reporters at city hall.
"We can't have 14 red vests telling people not to do what, you know, is common sense: not to pry the doors open," Watson said, referring to the red-vested OC Transpo employees who have been acting as ambassadors at stations since the Confederation Line opened last month.
"What people are doing, and I see it when I'm on the platform myself, they're rushing and running and trying to get in the door and holding it open when they don't have to because they can wait four minutes and another train will be coming," he said.
The city said Wednesday afternoon the Lyon station incident was caused by someone who was running to catch their train and tried to pry open the doors, while the Parliament station delay was caused by a rider holding the doors open with both hands.
Watson said the city has video footage of the Lyon station incident and is looking into the legal ramifications of releasing it publicly.
Hundreds of OC Transpo customers either caught replacement buses or walked the rest of the way to work after jammed doors caused significant delays on the Confederation Line Wednesday morning. (Giacomo Panico/CBC)
Watson wouldn't elaborate on what type of fine might be imposed, or how the city would be able to track down the alleged culprit.
Watson characterized Tuesday and Wednesday morning's chaotic commutes as "extreme growing pains," but said he understands customers are unhappy.
"This level of service is not acceptable. I'm frustrated. I was angry this morning," he said, adding that he's instructed John Manconi, the city's general manager of transportation services, and city manager Steve Kanellakos to come up with a solution to "this damn door issue once and for all."
Manconi later said at a press conference that OC Transpo was taking a number of steps to fix the problem.
Currently, the trains are set up so the doors close automatically after a certain period of time, but Watson said staff will be reviewing that system to see whether operators should be able to manually override the controls, or if more time should be allotted before doors close.
"Whatever the situation is, it has to be resolved because when one train goes down, it backs the whole system up and that adds to the anger and the frustration that people rightfully have."
Watson called on train manufacturer Alstom "to find out why is the system so fragile" that one jammed door can effectively shut down the entire line.
When there is a problem on the Confederation Line, OC Transpo brings in R1 buses to provide parallel service.
Coun. Allan Hubley, who chairs the city's transit committee, said nothing is off the table until the door problem is resolved, including continuing to run the buses regularly.