“The mayor and his staff put tremendous pressure on Stacey to give Harendra Singh a sweetheart deal, a process that started with a call directly from the mayor,” her lawyer, Mr. Walden, said in a statement, calling her a “hero” for pushing back against Mr. de Blasio’s effort on behalf of Mr. Singh. “She resisted that pressure and, as a result, City Hall seized control of negotiations with Singh.”

A Donor Seeks a Deal

Mr. de Blasio’s connection to Mr. Singh goes back at least as far as 2010, when Mr. de Blasio, who was then the public advocate, began raising money for what was considered a long-shot bid for mayor. Mr. Singh gave the de Blasio campaign $2,500 in December 2010 — becoming one of just 21 people who donated that much or more that year.

The following March, Mr. Singh held a fund-raiser at Water’s Edge and collected $5,750 in contributions from other people to Mr. de Blasio. By the time Mr. de Blasio was elected in November 2013, Mr. Singh, his wife, his parents, his employees and other associates had given the mayor a total of about $33,000.

Mr. Singh ran a group of restaurant and catering companies in New York City and on Long Island, and he had operated Water’s Edge since 2008. The restaurant, on a barge in the East River that was adjacent to a city-owned pier, leased the space from the city.

But Mr. Singh had been fighting with the city over the lease’s terms, including whether he was obligated to pay for the reconstruction of the pier. He also disputed the results of an audit that found that he had been underpaying rent, with arrears and late charges totaling about $1.2 million. And he was seeking a long-term renewal of the lease, which was to expire in 2017.

Mr. de Blasio made his first effort to help Mr. Singh in November 2011, arranging a meeting between the restaurateur and Edna Wells Handy, the DCAS commissioner at the time. Mr. de Blasio sat in on the meeting, which appears on his schedule as public advocate.

But the dispute persisted, and after Mr. de Blasio became mayor, Mr. Singh tried again — approaching him at the June 2014 event, a $1,000-per-couple fund-raiser for a congressman, Steve Israel, where the mayor was a featured speaker.