Investigators from Quebec's revenue ministry spent most of Thursday searching the Montreal offices of the controversial ride-sharing company Uber.

They carried out two search warrants obtained under the Tax Administration Act.

"Revenu Québec has reason to believe that tax fiscal law has been broken. So today we are searching to get more evidence," said spokesman Stéphane Dion.

"The goal is to obtain as much information as possible, and these documents will then be analyzed. After that, we'll be able to determine whether charges will be laid."

Revenu Québec investigators carried out search warrants at the Uber Montreal offices on Thursday morning. (Sean Henry/CBC ) The searches were carried out at two different locations — one in Old Montreal and another in Pointe-St-Charles.

Dion would not say what prompted their suspicions because the investigation is ongoing.

No charges have been laid.

When asked by CBC News to comment on the search, Uber Canada spokeswoman Susie Heath provided the following statement:

"We look forward to continuing to work with all stakeholders in Quebec to foster innovation, create jobs, and provide consumers with much needed affordable transit options."

City seized 40 vehicles

The raids were conducted just over two weeks after the City of Montreal announced it had seized 40 vehicles used by UberX drivers since the beginning of the year.

Uber's UberX service uses a smartphone app that links clients to drivers in privately owned vehicles, without a taxi licence, to provide rides that cost less than cab fares.

Montreal Mayor Denis Coderre stressed on Thursday it's not a question of using the technology — "it's a question of illegal transport.''

"If you give someone a lift and you have money, you call that a taxi,'' he said.

"There are permits for that and there are ways of doing it."

He noted the same problem with Uber is happening in other cities, such as Edmonton.

Coderre said UberX users must understand there are responsibilities when it comes to insurance and paying the taxman.

There's also the question of screening drivers.

Coderre said that's being done by the Montreal taxi bureau, which oversees the operation of cabs in the city.

"If it's illegal transport, there are consequences and the consequences are the seizure of a vehicle," Coderre said.