Just hours after the service started in Montreal, the city's mayor, Denis Coderre, said the popular app-based taxi service uberX is illegal.

UberX allows non-professional drivers to shuttle passengers around town in their own personal cars for a cheaper fare than standard cabs.

As of 10 a.m. Wednesday, Montrealers are able to select uberX as an option when ordering a ride through the Uber app.

The popular smartphone app connects drivers with passengers, letting people see the location of drivers and then sending them a request for pick up with a couple quick clicks.

The company says 100 drivers in Montreal have already signed up.

Its arrival on the market has proven controversial in a number of cities.

"Of course it's illegal," said Montreal mayor

Coderre said there are a number of existing rules surrounding transportation and uberX falls outside that legislation. He said it's in conflict with rules created by the Quebec Transportation Committee.

"Right now if they don't respect the rules, yes it's illegal, of course it's illegal," he said.

Coderre said he spoke with Quebec's transportation minister, Robert Poëti, this morning to discuss uberX.

Elsewhere, like Toronto, the legality of Uber has been challenged in court. The company denies any illegal activities, citing the lack of regulation for this type of transport.

uberX cheaper than standard cab fare

Uber, which was founded in 2009, began operations in Montreal nearly a year ago, allowing cab drivers who signed up to pick up additional fares they may not get through a dispatch company. The cab drivers using Uber charge a standard meter rate.

However, uberX allows drivers not licensed to operate as cab drivers the ability to use their own car to pick up passengers.

Uber says its uberX service costs users between 20 and 30 per cent less than a standard cab fare. The company takes 20 per cent of the fare, leaving the rest to the driver. Users' credit cards are automatically charged through the app — tip included — meaning no cash exchanges hands.

Cab drivers feel threatened

While the app is cheaper for customers, it represents a threat to Montreal taxi drivers. In San Francisco, where uberX is popular, some taxi drivers say they have lost half of their customers.

Some Montreal taxi drivers say the app creates unfair competition.

"I have to go through hoops and jumps to be a taxi driver," said one taxi driver, speaking to CBC News reporter Emily Brass. "It's not fair for me personally, that people are going to be able to compete without going through the same things."

Uber said it has an agreement with the RCMP for criminal background checks for its drivers, arguing that’s actually safer than conventional taxi drivers, who do not undergo regular checks.

Montreal will become one of 150 cities, including Toronto and Ottawa, where uberX is active.

The San Francisco-based Uber has been valued at an estimated $18 billion.