(Reuters) - New York City's public advocate, a Democratic mayoral candidate known for his liberal views, on Thursday sued the city to obtain data to determine if soaring fines are hurting small businesses.

Public Advocate Bill de Blasio said he has been stonewalled since May in his attempts to investigate whether city agencies - from the Departments of Health to Sanitation - have been guilty of "overzealous enforcement," in an apparent effort to boost how much money the city rakes in each year in fines, according to a complaint in Manhattan state court.

Mayor Michael Bloomberg ends his third and final term in 2013 and the race to replace him has already begun. De Blasio's law suit could broaden his appeal to the business community which has been wooed by another Democratic mayoral candidate, Council Speaker Christine Quinn.

"It is a smart political move by the public advocate, who is seen as far to the left, to try to move to the center by defending small businesses," said Hank Sheinkopf, a political consultant.

He said: "This is the Bill de Blasio moment - only he is in a position where he can take on the mayor this way," he said.

Political analysts said Quinn has held closely to Bloomberg's policies, though she has carved out a few specific issues, including her support for a so-called living wage bill, which boosts the wages paid by employers who get city subsidies.

New York City's public advocates probe the performance of city agencies and de Blasio said small businesses have flooded his office with complaints of being hounded for minor offenses and forced to pay "excessive" fines.

As an example of over-enforcement, de Blasio said a family-run grocery store in Brooklyn was fined $750 for violating rules about posting return policies on their cash registers.

CITY CLEANER, SAFER

Mayoral Spokesman Marc LaVorgna said the total amount of fines collected from individuals and businesses rose from $479 million in 2002 - Bloomberg's first year in office - to $817 million in 2012.

LaVorgna said 40 percent of the increase in fines came from construction violations, fire code violations, more restaurant inspections and a crackdown on illegal cigarette sales, along with other offenses.

"Restaurants are cleaner, construction sites are safer, fires have come down, and our streets are cleaner and safer than ever - that is a result of enforcing the regulations we have put in place and the laws the Council has passed," said LaVorgna.

Tickets for driving violations accounted for 60 percent or $204 million of the increase in fines in the last 10 years.

S. Elliott Henry, a 75-year old taxi driver who had just been through traffic court in lower Manhattan, said his $290 fine for turning left on Madison Avenue from 45th Street cost him three days pay.

For decades, New York City mayors, including Bloomberg, have denied setting quotas for fines to boost revenue. But de Blasio is seeking information on whether agency officials were told how many violations they should issue in a particular year.

"We need answers about what this ‘fine first, ask questions later' enforcement is doing to our small businesses and their ability to survive in this economy," De Blasio said.

The case is De Blasio v. Michael Bloomberg et al, Supreme Court of the State of New York, New York County, No. 12-103374.

(Editing by Anthony Boadle)