With his fundraising on behalf of state Senate Democrats under investigation, Mayor Bill de Blasio has insisted the funding mechanism his team used was both legal and commonplace and argued he’s the victim of selective enforcement. But at least one Democratic party leader believed such an arrangement was illegal, having turned down a similar donation. NY1's Bobby Cuza filed the following report.

It was September 2014. Republican Tom Croci was battling Democrat Adrienne Esposito for a Long Island state Senate seat. The state teachers' union, having already given the legal maximum amount to Esposito, wanted to cut an even bigger check to the Suffolk County Democratic Committee, which can transfer unlimited funds to a candidate.

"We believed it was illegal," said Richard Schaffer, head of the Suffolk Democrats.

Schaffer says because the money was meant for Esposito, it was an attempt to evade contribution limits, the same violation a state Board of Elections official says Mayor Bill de Blasio’s team committed in directing money to three upstate races around the same time.

"The fact that he told me, 'We want you to spend it directly on Adrienne Esposito,' that makes it illegal," Schaffer said.

Schaffer says he told the union no thanks, but got a check anyway, for $100,000. His committee rejected it, writing, "we are unable to deposit your check and are compelled to return it to you."

"They were annoyed," Schaffer said.

Much like de Blasio now, the union, New York State United Teachers, insisted the move was legal and told NY1 it has a longstanding record of meticulously adhering to the law.  

"They even said at one point, 'Well, we do this all the time.' And I said, 'Well, then I think you’re doing something wrong all the time. It doesn’t mean I have to do it,'" Schaffer said.

Schaffer said it’s the first and only time he’s ever heard of a county committee turning away a contribution like this. Indeed, usually, no one bats an eye at these types of transactions, which have happened plenty of times before, including on Long Island.

That includes $50,000 to the Nassau County Democrats to support recently elected state Senator Todd Kaminsky, reportedly traced to chief de Blasio fundraiser Ross Offinger. And in 2014, Republican state Senator Michael Venditto had $125,000 funneled to his race from former Senator Charles Fuschillo through the Nassau Republican committee.

Esposito, meanwhile, lost her race, but de Blasio’s troubles may provide a silver lining.

"I emailed out the first article about this and said, 'Hey. look at this,'" Schaffer said. "Two years ago, we did the right thing, and now, we’re not having FBI agents or DA investigators showing up at our house at six in the morning."