A group of St. Paul residents who say the city broke a promise to expand a downtown park have hired a lawyer and are raising money for a potential lawsuit.

Friends of Pedro Park Expansion say city leaders are going back on their own plans, as well as an agreement with the Pedro family, by proposing to sell a city-owned building instead of tearing it down to make way for a bigger park. Last week, members of the group were among several people who dropped out of city discussions about how to make the existing park space better.

“We want to fight for what we want the neighborhood to look like,” said Rod Halvorson, Friends of Pedro Park Expansion co-chairman.

In 2009, the Pedro family donated 0.45 acres along E. 10th Street to the city for use as a park. The city planned to demolish the adjacent Public Safety Annex building and combine the land beneath it with the donated land to create a larger park.

Last year, city officials began exploring the idea of turning the annex into an office development. The City Council, acting as the Housing and Redevelopment Authority, voted 4-3 in November to give the Minneapolis-based Ackerberg Group tentative developer status. Council Member Rebecca Noecker, whose ward includes downtown, was one of three no votes.

The council gave Ackerberg six months to study the building and decide whether to buy it. That decision is due next month.

The members of Friends of Pedro Park Expansion have argued that by going back on plans to expand Pedro Park, the city is deviating from its comprehensive plan and violating its charter, which protects acquired park land. Last week, the group hired Joe Lawder, a St. Paul attorney who specializes in real estate law, to explore legal options.

“There are processes the city has to undertake in this type of situation — for example, with respect to the Comprehensive Plan and with respect to what might be considered disposal of park property,” Lawder said in a statement, “and the question is whether it can avoid those requirements to sell property that was held out to be for park expansion.”

City Parks and Recreation spokeswoman Clare Cloyd said the long-term plan that applies to Pedro Park does not prohibit other uses, and the City Charter does not protect the annex land because it is not currently parkland.

Under the city’s plan, if it becomes office space, the existing Pedro Park will remain and the developer would pay to improve and operate it. Starting May 3, the Parks and Recreation and Planning and Economic Development departments have held design advisory committee meetings “to determine community needs and desires for Pedro Park,” according to the city’s website.

Several people resigned after the committee’s May 24 meeting, saying they weren’t given a chance to discuss the Pedro Park expansion.

“We gave them the benefit of the doubt and joined the process,” said Friends of Pedro Park co-chairwoman Kati Berg. “So we were surprised and saddened when nothing was presented on how to expand the park.”

Cloyd said the parks department is trying to figure out whether the people who resigned did so as individuals or as representatives of their organizations.

“We’re working to better understand the implications of those resignations right now, because we would love and welcome the groups to stay at the table even if those individuals choose not to participate,” she said.