TORONTO -- A pair of accordion players performing the summer hit "Despacito" while appearing on subway trains in Toronto have been warned to stop or risk being fined, the city's transit agency said Friday.

The two men have been spotted separately by commuters on various stretches of the subway system in recent days and videos of their performances have been circulating on social media.

The reaction to the busking is divided, with some online expressing their dislike, while others applaud the men for the entertainment during their commute.

The Toronto Transit Commission said enforcement officers came across the men a couple of times earlier this month and issued the warnings.

"We have not received any formal complaints through our customer service department," spokesman Stuart Green said Friday. "What we have seen is the online chatter and people posting videos."

Busking on trains is not allowed, Green said, and players must be approved before they can perform in designated areas on TTC property.

"We have a TTC subway musicians' program -- auditions of which are actually open right now," he said. "So if these guys are interested, they can apply to get a three-year licence to legally perform in the TTC system and earn some money at the same time."

Green said the men, who he identified as brothers, could be issued tickets if their on-train performances continue.

Transit customers "have the right to enjoy a relatively peaceful ride," Green said, adding that a common complaint from riders is about people playing their music too loudly without headphones.

The accordion players have received both love and loathing from their audiences.

One transit rider recently tweeted, "thank you accordion man on the subway for making this rainy commute home a little more entertaining."

Another tweeted, "I'm getting a little tired of this Despacito accordion player riding the subway. Nothing fails to sour me faster."

A Toronto-based professional accordion player who has seen the videos of the two men said "Despacito" isn't a particularly difficult song to play, but performing on a moving train can make a performance more challenging.

"The accordions are pretty heavy and it's probably a bit difficult because on the subway you need to hold on to something when there is an abrupt stop," said Claudio Santaluce. "It should definitely be a little bit tiring, because apparently they play for long periods of time standing up."

Santaluce added that he had personally enjoyed watching videos of the subway players.

"I might be biased because I'm a musician, but if I was on that train, I'd actually enjoy it and I'd tell all my friends about it," he said.

"Despacito," by Luis Fonsi, featuring Daddy Yankee, became the most viewed clip of all-time on YouTube last summer and the most-streamed track of all-time. However, the record-breaking video did not feature vocals by Canadian pop star Justin Bieber that appeared on a remix.