The Toronto Transit Commission is dealing with yet another case of rider frustration after a bus driver was videotaped leaving his bus and taking what appears to be an unscheduled coffee break at Tim Hortons.

The video shows an unidentified driver step out of the coffee shop and walk into his bus, where he then confronts the passenger shooting the video.

An argument between the driver and the passenger ensues, and the driver then states that the bus is out of service.

The video was taken on the Dufferin bus route near Castlefield Avenue, north of Eglinton Avenue, on Saturday morning.

Responding to the latest public embarrassment for the commission, TTC chief general manager Gary Webster issued a stern warning letter to employees Saturday afternoon about the importance of customer service.

"We are in the customer service business, but some of the behaviour our customers have encountered recently would suggest otherwise," Webster writes.

"As employees, you -- and you alone -- are accountable for your actions. The culture of complacency and malaise that has seeped into our organization will end."

While Webster also writes that plans are underway to "address systemic issues regarding customer service," he implored TTC operators to change their ways.

In an email to media outlets, TTC spokesman Brad Ross said that the commission won't be responding to any more interview requests and would not comment on photos or videos taken by riders.

Ross added that any riders with complaints can call the TTC directly at 416-393-3030 or make a written complaint on the TTC's website.

The TTC has suffered weeks of negative publicity, which peaked last month when a photo showing a fare collector apparently sleeping on the job became a hit on the Internet.

Since then, other photos of apparent employee misbehaviour have stoked the anger of riders.

Late last year, the commission was slammed for the way it handled a controversial fare hike.