New York Mayor Bill de Blasio’s campaign attorney Sunday accused the state’s top election investigator of trying to “selectively criminalize” legal political fundraising efforts in a January memo alleging he and his aides broke campaign finance laws.

Laurence D. Laufer defended the mayor’s 2014 fundraising in a seven-page letter to Risa Sugarman, the chief enforcement counsel of the state Board of Elections, saying she misunderstood campaign finance law and her office “was treating a coordinated political party effort to elect a majority to the State Senate as some kind of criminal conspiracy.”

He also accused Sugarman of leaking the Jan. 4 internal memo that surfaced Friday in a “politically motivated act” that violated her “nonpartisan, independent function.”

In the memo to the election board, Sugarman said de Blasio and his political aides broke state campaign-finance laws in 2014 when coordinating fundraising efforts for Democratic state Senate candidates, as part of an unsuccessful effort to reclaim control of the chamber.

“I have determined that reasonable cause exists to believe a violation warranting criminal prosecution has taken place,” Sugarman wrote in the memo. “. . . The violations discovered by this investigation can only be described as willful and flagrant.”

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Sugarman said de Blasio had conspired with the New York Hotel Trades Council union, the United Federation of Teachers, and political consultants to channel at least $971,000 in 2014 to three upstate Democratic senate candidates and skirt campaign-finance laws by having donors contribute to party committees who would then transfer the money to each candidate’s campaign account.

According to a source, the board unanimously voted earlier this year to refer the matter to the Manhattan District Attorney’s Office for potential criminal prosecution, at the recommendation of Sugarman, who was appointed to the role of reviewing election law complaints in 2014, by Gov. Andrew M. Cuomo. She did not immediately return an email Sunday seeking comment.

In his letter, Laufer said de Blasio’s fundraising methods were entirely legal. Both Republicans and Democrats have long solicited donors to contribute to local and state political parties, who then transfer the money to individual candidates, Laufer wrote. Under state law, donors can contribute a maximum of $102,300 to a party committee, compared to $10,300 for an individual candidate. There is no restriction on the amount of money a party committee can transfer to an individual candidate.

“There is nothing novel about the 2014 Democratic Party campaign to elect Democratic candidates to the State Senate other than your attempt to selectively criminalize it,” Laufer wrote of Sugarman’s efforts.

Laufer also accused Sugarman of violating the state’s Freedom of Information Law, which instructs state employees to not release records to the public “compiled for law enforcement purposes, and which if disclosed, would “interfere with investigations or judicial proceedings, or “deprive a person of a right to a fair trial.”

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De Blasio has been buffeted for the past month by a series of leaked reports about investigations into how he funded the 2014 campaigns and whether donors got preferential treatment.

The activities of de Blasio donors Jeremy Reichberg and Jona Rechnitz, Brooklyn businessmen who gave to the mayor or his campaigns, are at the center of several investigations, including those of Manhattan U.S. Attorney Preet Bharara as well as the city’s comptroller and Department of Investigation.

The pair are also the focus of an investigation into whether top brass in the NYPD took gifts in exchange for favors, according to sources.

In addition, investigators are examining contributions to a nonprofit created to advance de Blasio’s policy agenda, as well as a land deal involving the removal of a restrictive deed on a former AIDS housing property that was then sold at a profit of millions of dollars to become luxury condominiums. A top de Blasio fundraiser, James Capalino, had a lobbying role in the deal.

Also last week, a leaked report said Bharara was examining the circumstances surrounding de Blasio’s unpopular and so far failed efforts to ban horse-drawn carriages from Central Park, after carriage foes showered campaigns benefiting the mayor with six-figure contributions.