For the first time since their plan to build a city in Solano County became public, representatives of California Forever went to a local government and asked for permission to do something.

For the billionaire city-builders, it was a big-time bust.

In a unanimous decision Tuesday evening, the City Council of Rio Vista — a charming delta town of 10,000 that would be the closest city to where the new metropolis would sprout from dry farmland — rejected the idea that it would allow the city’s outside legal counsel to also represent California Forever, the developer’s parent company.

The law firm of Kronick, Moskovitz, Tiedemann & Girard, which has provided legal counsel to Rio Vista since 2011 — most small California cities hire outside firms rather than fund their own legal departments — had asked the city council for permission to also represent California Forever in its process of securing the water rights for the still unnamed, built-from-scratch city.

It was a resounding no.

While the vote was small potatoes in the context of a group that has spent $800 million on purchasing 50,000 acres and is determined to spend billions more to create America’s next great city, it demonstrated the political obstacles that California Forever will need to clear as it tries to convince the majority of Solano County of the wisdom of a project that would transform a corner of the Bay Area still mostly made up of farms and small towns like Rio Vista.

In its request, the firm, KMTG, promised it would create a separation between lawyers working for the city of Rio Vista and those helping California Forever secure water rights for a new city that could become home to 100,000 residents or more.

KMTG attorney Olivia Clark said that if any conflict arose the firm would represent the city, and not the developer. She said KMTG’s expertise in Solano County development issues, and water rights, could be a benefit to Rio Vista.

“We bring a lot of experience and institutional knowledge — that unique background will help both entities moving forward … rather than California Forever finding some hotshot L.A. firm to phone it in,” she said. “I think it’s better to know your neighbor and know they have competent legal counsel representing them. … What’s the cliche? It’s better to know your adversary than take a gamble.”

In a memo on the topic, KMTG partner Mona Ebrahimi said there was “no present conflict between California Forever and Rio Vista” in terms of water rights, but she allowed that there might be down the road.

“The concern is that Rio Vista might oppose California Forever’s efforts to orchestrate water supplies for future land-use projects and might oppose California Forever’s efforts to obtain land-use approvals allowing such projects,” she wrote.

Currently, Rio Vista relies on groundwater pumped from the Solano Subbasin of the Sacramento Valley Groundwater Basin. Although, if that resource is depleted, it could put the city in conflict with the water sources California Forever is looking toward, including the Sacramento River.

But neighbors were not convinced, and neither were elected officials.

After public comment in which all of a dozen or so Rio Vista residents urged the council to reject the idea, the five member body quickly put the kibosh on the request.

Resident Kenny Paul said allowing the firm to represent both sides would “put the city in a bad position.”

“We are not going to be able to stop Flannery, ultimately, but do we extend a hand to them in welcome or do we say, ‘No thanks? ’ ” said Paul. “The fact that they would go after the same counsel we have, who are experts in water rights fights, just speaks to their continued bad faith.”

Resident Bill Mortimore said the law may be well-intentioned but that ultimately there will be conflict “when Flannery comes in and throws a half a billion on the table.”

“Our legal representatives have good intentions, but money talks. I can picture a conflict arising and them walking in with a checkbook,” he said.

Jeannie McCormack, a third generation rancher who rejected Flannery’s efforts of a buy-out of her family’s 3,700-acre ranch, warned against the firm’s request. She said California Forever’s current legal representation — Skadden, Arps, Slate, Meagher & Flom LLP — would provide plenty of legal firepower without also enlisting Rio Vista’s lawyers.

“They have a very high-falutin and well-known legal firm … they don’t need anyone else,” she said. “They will try to weaken Rio Vista and we won’t know what their aims are because they are very closed-mouthed.”

Former Solano County Supervisor and project opponent Duane Kromm said the vote was significant because KMTG is one of the few firms that knows Solano County water rights issues inside and out.

“There is a limited subset of law firms highly specialized in California water rights,” he said.

He said the lopsided dynamic of the fight over the future of eastern Solano County would continue to test the small cities in the area.

“It’s not David vs. Goliath,” he said. “It’s David vs. an aircraft carrier.”

California Forever did not respond to a request for comment.