A move by the Board of Supervisors to ban virtually all picnic reservations at city parks could blow a hole in the Recreation and Park Department budget and change the decades-old way groups and organizations have used the city’s open spaces.

The furor began on a sunny afternoon last month, when an inconspicuous blackboard popped up on Dolores Park’s lawn. “Make a reservation for a picnic space!” it read in pink marker.

Within hours, a snapshot of the announcement had been re-posted on social media thousands of times. San Francisco’s easily ignited outrage had been sparked. More than 18,000 people signed a petition.

A resolution sponsored by progressive Supervisors Jane Kim, Aaron Peskin, John Avalos, Norman Yee and David Campos is calling on the park department to stop renting out Dolores Park and other public space for events ranging from picnics and weddings to birthday parties and family reunions.

That could be very bad news for city finances, because the park department relies heavily on the money these events bring in. One-third of the department’s operating budget is earned, which includes payments for the reserved events. The permit money brought in, about $360,000 annually, goes to lawn maintenance and trash disposal.

“What do we do with that money?” said Rec and Park Director Phil Ginsburg. “We invest it in our parks system. The money that we earn basically pays for all of our gardeners, custodians and recreation staff. Earned revenue subsidizes the services we provide.”

But to many, the permit system seems like another example of how San Francisco is pricing out the lower and middle class. As money flows into the city, more public services are seemingly becoming privatized. Tech shuttle buses clog Muni stops, and company employees can rent soccer fields normally used by neighborhood children. The idea of charging as much as $260, plus a $200 deposit, to rent a patch of public grass angers many residents.

“I find it very troubling that we have even considered a proposal to charge the general public to enjoy the grass in Dolores Park, or any other parks for that matter,” Peskin said. “We all have the right to enjoy the city’s precious open space and picnic without having every square foot and blade of grass privatized and micromanaged.”

Common practice in parks

What has gone unmentioned is that the sale of permits has long been a common practice in San Francisco’s parks. Last year, Rec and Park issued about 7,000 picnic permits, most of them used for family events and school gatherings. The system in Dolores Park — which was on a hiatus after the green space’s months-long, $20.6 million renovation — was rejiggered from the previous nine rental slots to seven and reintroduced this spring as a “pilot program.”

That caused confusion, Ginsburg said. The phrasing was different only because the department was testing different locations within Dolores Park to see how permits would affect circulation, he said.

The program at Dolores Park has since been suspended, and only picnic tables, which seat about eight people, are available for reservation.

“To be clear, reserving picnic tables and lawn areas is common practice throughout San Francisco’s park system and has been for decades,” Supervisor Scott Wiener said. “Indeed, in Dolores Park itself, it has long been the case that a few areas of the park can be reserved for picnics and parties. ... Rec and Park is simply reinstating the previous state of affairs.”

In parks across the country, lawn permits are a common way of reserving space. In San Jose, residents pay from $100 to $400, while in San Mateo, it costs $40 to $300, and in Marin County, it’s $75 to $225. Last year, Rec and Park made $362,000 from group picnic permits, or the equivalent of the salaries of two gardeners and two custodians.

Recovering expenses

A reservation system helps ensure space is available for birthday parties, weddings and nonprofit events, Ginsburg said. It also helps recover costs associated with large gatherings, he said.

The 4/20 event in Golden Gate Park cost taxpayers $50,000 to clean up, Rec and Park documents show. The Valentine’s Day pillow fight at Justin Herman Plaza incurred similar costs. Neither of the events requested a permit, said Elton Pon, a spokesman for the park department, leaving the city on the hook for the costs.

“People reacted to (the Dolores Park plan), and it touched a nerve,” Ginsburg said. “It’s important to spend some time talking about what (the permit system) was and wasn’t. Public-private partnerships have helped reinvigorate our system. We need to fund our park system, and what we do is no different than New York City or Chicago. It’s not selling space to the highest bidder. It’s a picnic reservation.”

A similar reservation system, with different costs, is used for city athletic fields.

The resolution is awaiting action at the Public Safety and Neighborhood Services Committee before heading back to the Board of Supervisors for a final vote this summer.

And in the meantime? The grass is first come, first served at Dolores — no price tag involved.

Lizzie Johnson is a San Francisco Chronicle staff writer. Email: ljohnson@sfchronicle.com Twitter: LizzieJohnsonnn