TORONTO -- As the transit agency in Canada's most populous city prepares to do away with its decades-old payment system, Toronto's mayor and the union representing transit workers are asking the Ontario government to step in and fix what they describe as faulty technology in the higher-tech replacement.

December marks the last month commuters will be able to use Metropasses on the Toronto Transit Commission system as the network of buses, streetcars and subways switches over to Presto, an electronic tap-card payment system used mostly in southern Ontario. Transit tickets and tokens are also set to be phased out in mid-2019.

Some, however, have raised concerns that the technology isn't reliable and won't withstand the surge in Presto users in the coming months and beyond.

Toronto Mayor John Tory is urging the province to "get this program into shape to make sure it provides the reliable service that transit riders deserve," his office said Sunday.

Tory's spokesman, Don Peat, said the complete elimination of tickets and tokens "cannot happen until Presto is working well on all fronts."

"Mayor Tory fully supports the modernization of our transit system but he is also frustrated at the Presto implementation process so far, and while somewhat improved, the service we are receiving is still well short of satisfactory," Peat said.

Meanwhile, the union representing roughly 11,000 frontline TTC employees has sent a letter to Premier Doug Ford asking that the provincial government take "immediate and urgent action" to address what it sees as an unreliable system with machines that regularly break down.

"We want (the government) to address the fact that the Presto system has failed," said Kevin Morton, spokesman for the Amalgamated Transit Union Local 113. "It's just a debacle."

He said the union believes the TTC won't be able to handle the influx of Presto users as the card readers regularly fail and take too long to repair. Those problems could also lead to a loss of revenue, which could later be mistaken for a drop in ridership, he said.

Morton said the union has received "hundreds" of messages from its members about commuters not being able to pay because card readers are broken. A number of TTC workers are quoted anonymously in the union's letter to Ford, saying the readers fail daily and sometimes take days to repair.

The union said it had a "very productive" meeting with Tory on the issue on Thursday. Peat confirmed the meeting took place and said the mayor appreciates the union raising its concerns.

The provincial government, the TTC and Ontario's transit agency, Metrolinx, all expressed confidence in the Presto system.

Andrew Koolsbergen, a spokesman for the ministry of transportation, said Metrolinx has placed additional staff in stations to assist travellers during the transition.

The TTC will also have more staff posted at Presto vending machines, as well as maintenance workers to fix readers "within a reasonable amount of time," spokeswoman Heather Brown said.

Brown said Presto readers are mostly fixed within 24 hours, and noted buses and streetcars have two. If both readers are down, riders are told to pay at their destination, she said. Those caught evading payment could be fined up to $425, she said.

Metrolinx, which oversees Presto, said the reliability rate for card readers on buses and streetcars is averaging 98 to 99 per cent each week.

Public reception for Presto has been mixed, with some welcoming the streamlined system and others decrying the change.

Rohan Kekre, 30, said the transition is a good move. "It's just so convenient because you just have one card and it's easy to tap," said Kekre, who has a Presto card and takes transit daily.

He recalled coming across a malfunctioning card reader on a bus a few weeks ago and said the driver allowed him to ride for free.

Illia Khairetdov, who only takes the TTC twice a week and mostly pays cash, said he was put off by the process of buying and regularly loading the card with fare money.

"Honestly, I'm annoyed that I'll eventually have to buy a Presto card," the 23-year-old said.

Brown, the TTC spokeswoman, said Presto tickets will eventually be an option for infrequent TTC riders or tourists. She said a single ticket or day pass is expected to become available in June 2019.

More than 78 million monthly Metropasses have been sold since they were introduced in 1980 for a cost of $26, the TTC said. Today, they cost nearly $150, and after Dec. 31, monthly transit passes will only be available through Presto.

The TTC began offering Presto as a payment method in 2011, and Brown said more payment options such as the monthly pass have become available through Presto over the past few years.

The TTC had about 1.7 million customers each weekday last year, according to its website. Metrolinx spokeswoman Anne-Marie Aikins said there are about 1.3 million Presto card holders who use the TTC and approximately 800,000 taps on card readers per day.