Quebec City is cracking down on a flourishing underground hotel industry.

City council voted Monday night to raise fines for operating an illegal hotel from $100 to $1,000 for a first offence, and from $200 to $4,000 for repeat offenders.

At least 50 property owners are breaking municipal zoning laws by renting apartments or rooms to tourists in the Old City, city spokeswoman Françoise Roy said.

And many more may try to make an extra buck as Quebec gets ready to welcome thousands of tourists for the 400th anniversary celebrations of the city's founding.

The practice is wrong because property owners aren't paying taxes on the rentals, and the additional traffic is bothersome for residents, Roy said.

It also threatens quality of life inside Quebec's fortified city, said Louis Germain, president of a local citizen's group. "Old Quebec will be like a lot of other heritage cities in the world: empty, Disneyland, no residents, nothing; a false city, a decor."

Most tourists who rent these kinds of rooms don't even realize they're illegal, Germain said.

But the fines will probably discourage aspiring hoteliers, he said.

"With stronger deterrents, I think that the individual who is trying to make $30,000, $40,000 a year, if he's facing $20,000, $30,000 in fines, because he got caught several times at $4,000 a shot, he'll think twice," he said Monday.

It's difficult for inspectors to crack down on illegal rentals because they're brokered on the internet and usually involve a short-term stay, the city said.

More inspectors will be assigned to investigate illegal room renting this summer.

But it may not have much of an impact this season because of the difficulties in proving that money has changed hands.