At first, the Tempest Bar's Tony Cooney welcomed Off The Grid, a convergence of five to six food trucks that parked several feet away from his Natoma Street restaurant every Wednesday.

"Our lunch crowd was down by about 75 percent," he said. "But it was cool. They were bringing people to the area and it was good for the community."

But when Off The Grid's food trucks began coming on Fridays, too, Cooney's business plummeted to the point of serious concern.

Like Cooney, a groundswell of San Francisco merchants, property managers and restaurant owners say the rise of the food truck phenomena is eating into their businesses and they want a fairer playing field. Many blame recent city legislation, which they say gives an unfair advantage to food trucks, and are asking that the supervisors amend the law.

The objective of the rules, enacted in March, was to accommodate the growing popularity of the mobile food industry by streamlining the permit process and making the cost less prohibitive. The price of obtaining permits used to run upward of $10,000. Now, it ranges from $800 to $3,700, depending on how many locations the operator has applied for, according to the program's overseer, the San Francisco Department of Public Works.

But opponents complain that the law doesn't limit the number of food trucks that can operate in a specific location and that authorities aren't enforcing time limits for how long a truck can park. Nor are they prohibiting mobile food vendors from selling in front of other quick-serve brick-and-mortar restaurants.

"There's no faith in the process," said Rob Black, a lawyer and executive director of Golden Gate Restaurant Association, a trade group that represents eateries as well as food trucks. "Right now, it's creating a lot of financial insecurity and legal uncertainty."

But city officials and food truck representatives argue that the law provides strict guidelines, including requiring mobile vendors to notify nearby businesses when they are in the area. It also prohibits parking within 300 feet of a business selling similar food and requires vendors to adhere to all parking regulations.

"If we find out that they're not following the rules, we can and will revoke their permits," said Gloria Chan, a spokeswoman for Public Works. While there are no inspectors per se, Chan said businesses should have no qualms reporting food trucks in violation.

There's no question that food trucks are increasing in number and popularity around the city. Since March, 85 companies have submitted applications for mobile food permits. Of those, 16 have been approved, 12 are pending approval, 20 are scheduled for public hearings, 20 are in various stages of the permit process and the rest have just started the application procedure, Chan said. Before the law went into effect, the San Francisco Police Department, which used to regulate the process, had granted approximately 200 permits, which are still in effect.

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"There's no limit," Black said of the number of permits. "And if the city continues to ignore this, they're going to reach the point of no return. We need the legislation amended."

But Gillian Gillett, an aide to Supervisor Scott Wiener, whose predecessor Bevin Dufty spearheaded the new rules, said at this point there is no plan to change the law.

"We're open to discussion and reviewing what needs to be done," she said. "It's a complicated set of issues."

Karen Smith is a property manager for TRI Commercial Real Estate who is trying to prevent at least two food trucks from parking on California Street, where four of her tenants run quick-serve restaurants. She said if something isn't done, food trucks are going to destroy the businesses.

"On average my tenants pay $9,000 (a month) in rent," she said. "The trucks want to park here five days a week from 10 a.m. to 3 p.m. As far as we're concerned that's permanent, not mobile. And they don't have to pay rent."

Black agrees the trucks have an unfair advantage.

"The city in essence is subsidizing the mobile food industry by giving them a free right of way," he said.

Others argue that there's a great demand for the variety and prices the trucks offer, and that the trucks have every right to compete in a free market.

"It's no different than if a brick-and-mortar restaurant moved in on the same block," Gillett said.

Matt Cohen, founder of Off The Grid, which in addition to organizing food truck events is a consulting firm for the mobile catering industry, said that with so few operators receiving permits since the law went into effect, it's too early to tell what consequences it will have on brick-and-mortar restaurants.

"For anyone to be passing judgment at this point is premature," he said.

Black, however, is concerned that most of the applicants want permits for the Financial District and South of Market and that the restaurants in those neighborhoods will feel the brunt of the competition.

"There are no written rules on whether you can have one, two, three or even more trucks on one block," he said. "It's not addressed in the law."

Ken Cleaveland, director of government and public affairs for the Building Owners and Managers Association, argued that allowing mobile food vendors downtown doesn't fill a need.

"The intention of the legislation was to bring vitality and life to underserved areas of the city," he said. "Downtown isn't underserved by food businesses."

The Tempest's Cooney said he doesn't want the Off The Grid trucks moved, but would like to reach a mutual agreement so that everyone benefits, including customers. If they don't come up with a plan soon, he said, his business will die.

"I've put $30,000 into my kitchen - for a dive bar, that's a lot of money," Cooney said. "But now, two days a week, I have no one in here. I had to cut my labor way down just to make it."

Cooney and other South of Market restaurateurs have signed a petition, which they plan to submit to their district supervisor, hoping to open lines of communication with the Off The Grid team. Cohen said he "welcomes a conversation and would be willing to consider any changes."

For the sake of all his members, Black hopes the city can work out the differences.

"Everyone just wants a fair playing field."