With the mayor facing a wide-ranging investigation into his fundraising practices, one likely question is whether donors received, or were promised, official favors. And while much attention has been focused on donors opposed to the horse carriage industry, no one has been more generous with their contributions than real estate developers. NY1's Bobby Cuza filed the following report.

Mayor Bill de Blasio may not seem like a great friend to the real estate industry, given his aggressive efforts on behalf of tenants and affordable housing.

"For too many years, the real estate developers called all the shots in this city, and that has to change," the mayor said.

But when it comes to the Campaign for One New York, the controversial nonprofit the mayor created to promote his policy agenda, there’s been no greater friend to him.

"The real estate industry is the single-most important industry for Bill de Blasio when it comes to fundraising. There’s no question about it," said Konrad Putzier, reporter with The Real Deal.

The mayor himself, or any other candidate for city office, is actually prohibited from taking donations from any corporation, and individuals who do business with the city face strict limits under the city’s stringent campaign finance rules, allowed to give only $400 to a citywide candidate. But no such limits apply to the Campaign For One New York, and numerous developers having given huge sums around the same time they were seeking land-use approvals. Two Trees, for instance, which won a rezoing to redevelop the Domino Sugar factory project, later gave the campaign $100,000.

Insiders note the real estate industry has always been an active political contributor, and there’s no evidence in any case of a quid pro quo. But Putzier, who’s reported on the topic for the Real Deal, a real estate-focused magazine, says it’s also clear not all these developers are supporters of the mayor’s policies.

"One famous example is David Walentas of Two Trees Development. He was quoted as saying that de Blasio is a disaster for the city. He compared his administration to North Korea. And lo and behold, couple months later, a LLC tied to his company gave $100,000 to de Blasio’s Campaign for One New York," Putzier said.

Meanwhile, despite all the investigations revolving around his fundraising, de Blasio is continuing to raise money for his re-election campaign next year, inviting supporters to a fundraiser at a Brooklyn bowling alley in two weeks, headlined by the comedian Louis C.K.