In a move that throws a curveball at the Oakland A’s, the city of Oakland has sued Alameda County to block the county from selling its ownership in the 155-acre Coliseum arena site to the baseball team, which hopes to develop that land to help fund a new waterfront ballpark.

A’s President Dave Kaval said Monday that the team was “completely blindsided” and “very disappointed” by the city’s lawsuit, filed Friday in Alameda County Superior Court.

The suit also apparently upset Oakland Mayor Libby Schaaf, who said she hopes the city “suspends” the suit, which was filed by the city attorney’s office at the direction of the City Council.

“Our city and county governments should work with each other, not against each other,” Schaaf said. “I hope the council suspends this suit so we can all collaborate together on a beneficial future for the Coliseum.”

Oakland asked a judge to issue an injunction to stop the sale of the land and to force the county to instead enter into negotiations to sell the land to the city. The site, the largest swath of publicly owned land in Oakland, is jointly owned by the city and the county, and the A’s have agreed to pay the county $85 million for the county’s 50% share.

Oakland officials accused the county of violating the Surplus Lands Act, a state law that requires publicly owned surplus lands to be considered for affordable housing before the lands are sold or leased.

The Surplus Lands Act requires that public agencies negotiate with other interested public agencies first, Oakland City Attorney Barbara Parker’s office said.

The law requires the county to negotiate “in good faith” for at least 90 days, but the county “has not complied with this mandate,” the complaint alleges. It states that if the sale goes through, any plans to develop the space into affordable housing is “extinguished.”

County officials have said that they have been trying to get out of the sports business and had been in discussions with the city since 2015 to sell the county share — to no avail.

The city, however, claims that county officials did not negotiate in good faith and were already privately negotiating a sale with the A’s.

“The Coliseum properties are Oakland’s largest public land parcel, and it is imperative that the properties are developed first and foremost for the benefit of the people of Oakland and Alameda County,” Parker said. “The city has declared its commitment to develop the Coliseum properties to achieve their highest and best use for the public good.”

If a judge does issue the injunction, the county could still choose to sell to the A’s after negotiating with the city.

“Obviously, we are really disappointed that the city has gone to court to try and block the transaction with the county,” Kaval said. “We are reviewing the suit to see what it means, but like I said, we are super disappointed with no advance warning.”

It’s unclear how the lawsuit could impact the team’s plans to build a privately financed ballpark at Oakland’s Howard Terminal.

“We are reviewing the suit to figure out exactly what the complaint is about right now,” Kaval said.

Parker said the complaint “has nothing to do with” the proposed ballpark project.

Members of the Alameda County Board of Supervisors did not immediately return a request for comment.

In April, the the supervisors voted unanimously to sell their share of the Coliseum site to the A’s.

Prior to the vote, Schaaf implored the board to consider the impact of a sale to neighbors of the site.

In August, Oakland City Council President Rebecca Kaplan and Vice Mayor Larry Reid sent a letter stating that the deal between the county and the A’s didn’t have any provision for building a ballpark for community benefit to be included in the sale.

Board of Supervisors President Richard Valle responded to a letter sent by the city saying that since 2015, the county has held 33 meetings and pieces of correspondence with Oakland politicians and city staff regarding a potential sale of their Coliseum share.

“We hope that filing this lawsuit will help both agencies to realize a deal that ensures the highest and best use of the properties in the long term, that may include but is not be limited to affordable housing, jobs, retail, commercial space, open/recreational space, professional sports and hospitality,” Parker said.

The A’s are the last remaining professional sports team in Oakland with the departure of the Warriors and soon, the Raiders. The A’s have been trying for years to build a new ballpark in Oakland.

Phil Matier and Sarah Ravani are San Francisco Chronicle staff writers. Email: pmatier@sfchronicle.com, sravani@sfchronicle.com Twitter: @philmatier, @SarRavani