NEW YORK (CBSNewYork) — An investigation into Mayor Bill de Blasio’s fundraising efforts is reportedly expanding to include those behind a push to ban horse drawn carriages in the city.

Federal and state prosecutors are looking into whether or not de Blasio gave favors to two donors who opposed Central Park’s horse drawn carriages and were also looking to develop valuable West Side property where the stables sit, WCBS 880’s Marla Diamond reported.

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Wendy Neu and Steven Nislick, a real estate developer, gave more than $100,000 to de Blasio’s election effort.

Sources told CBS2’s Marcia Kramer that a flurry of subpoenas have been issued as part of what is being described as the preliminary stages of a wide-ranging probe into various fundraising activities by de Blasio, reportedly trying to determine whether state election laws were circumvented and whether promises were made in exchange for the donations.

De Blasio said “we will fully cooperate with any investigation.

“Everything we’ve done is legal and appropriate. I’ve said many times that we’ve held ourselves at a very high standard of integrity,” the mayor said.

CBS2 first reported about the probe nearly two weeks ago, which includes NYCLASS activists Neu and Nislick and de Blasio’s former campaign treasurer Ross Offinger.

De Blasio has reportedly met with with Nislick and Neu four times since he took office.

“The broad discussion was always about how we achieve the change in my platform, what we wanted to get the horse carriages off the streets,” the mayor said.

When asked by Kramer if he ever talked to them about raising money for him, de Blasio responded, “At City Hall I talked to them about how to get horse carriages off the street, period.”

Nislick denies he had his eye on the West Side property where the horse stables sit.

“Mayor de Blasio holds his Administration to the highest standards of integrity,” Karen Hinton, a spokeswoman for the mayor, told The Wall Street Journal. “We will cooperate fully with the investigations.”

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A spokesperson for NYCLASS, the animal rights group founded by Neu and Nislick, released a statement:

NYCLASS has not heard a word in any way, shape or form from the U.S. Attorney or the Manhattan District Attorney regarding the reported investigation into the mayor’s fundraising efforts. We have absolutely no reason to believe the story is true or accurate, and it’s important to note that today’s media report doesn’t say anything specific as it relates to the government’s alleged examination of NYCLASS. We have seen this type of reporting before: Two years ago, media reports said the FBI was “looking into” NYCLASS. But in the two years since that story ran, we have heard absolutely nothing from the FBI. Zero. So NYCLASS gets dragged through the mud publicly yet again without any reason to believe the story is accurate.

Steve Nislick and Wendy Neu founded NYCLASS because they care about animals. Their only agenda is the proper treatment of abused animals in this city. It’s one they deeply believe in, and will continue to fight for. It’s as simple as that. They have made clear over and over again that they have no interest in anything else, and have stated directly they have no interest in the real estate where the horse stables are currently located. That myth has become fact in some quarters simply because it has been reported over and over again as fact, when it is a lie.

If ever contacted by the U.S. Attorney or the DA, or anyone else in government, NYCLASS intends to answer any and all questions, and fully cooperate. But again, we have not been contacted, and have never been contacted by the FBI, U.S. Attorney or the DA.

De Blasio’s effort to move the horses from the West Side to Central Park and severely limit the horse drawn carriages failed earlier this year.

Neu and Nislick haven’t been accused of any wrongdoing, neither has the mayor, Diamond reported. The investigation is part of larger probe into whether the mayor’s fundraising efforts circumvented state election laws and whether donors were promised or given favors, the Journal reported.

The report comes after other federal probes focusing on the NYPD and de Blasio’s fundraising have so far led to one arrest and several officers to be reassigned or disciplined.

The federal probe is looking into whether police officers accepted gifts from businessmen with ties to the mayor.

It has centered on two businessmen who have ties to de Blasio’s campaign. Jeremy Reichberg and Jona Rechnitz both served on de Blasio’s inaugural committee and either donated or raised money for him.

The mayor previously said he was not happy with the expanding number of people caught in the investigative web and also downplayed his relationship with Reichberg and Rechnitz.

The mayor has said he has not accepted money from them for his re-election.

“I hold myself and my administration to the highest standard of integrity,” de Blasio said. “We are very, very careful about doing things in a legal and appropriate manner. We’re very, very careful about disclosing the support we get. We disclose everything, and we welcome questions about it.”

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Kramer previously reported that Barry Berke, the attorney who represented former NYPD Commissioner Bernard Kerik in his federal corruption case, is now representing de Blasio in the campaign fundraising investigation.