NEW YORK (CBSNewYork) — The head of the Suffolk County Democratic Committee had a terse message for Mayor Bill de Blasio Monday – “You’re wrong.”

As CBS2 Political Reporter Marcia Kramer reported, Richard Schaffer said it is not a “normal thing” to accept checks that appear to skirt campaign finance laws.

Schaffer said he took immediate action when Steve Allinger, a lobbyist for the New York state teachers’ union, tried to give him a check for $100,000. The check was issued on the proviso that it be earmarked – sent to 2014 Democratic state senate candidate Adrienne Esposito.

“My take was that it was illegal,” Schaffer said. “If I had taken the action and followed with what they had said they wanted me to do, that I would be committing a violation of the campaign finance law, which is a criminal violation.”

It was a surprising disclosure, since in 2014, Mayor de Blasio was involved in a frantic campaign to help Democrats take control of the New York State Senate. The Esposito race was apparently key to his success.

“It was one of the targeted races that was being targeted in order to flip the senate to the Democrats,” Schaffer said.

The actions of team de Blasio are being investigated by state and federal prosecutors to see if donors, including labor unions, made large contributions to local county committees to evade the $10,300 individual donation limit.

When CBS2’s Kramer first asked de Blasio about his fundraising in October 2014, the mayor said his actions were completely acceptable campaign practice.

“It’s something that’s been going on a long time in this state,” de Blasio said at the time. “It’s a normal thing to provide support for party organizations.”

De Blasio denied that any “pay to play” was involved in his fundraising efforts.

“There’s nothing new here,” de Blasio said. “For years and years, people have supported party organizations.”

Schaffer, an attorney, said he disagreed – and that is why he sent the contribution back.

“At the outset, as soon as they said, ‘We’re sending you the money and we want you to spend it on Esposito,’ I knew that that was a violation,” Schaffer said.

Kramer asked Schaffer whether he was ever tempted to take the money, given that the race was hotly contested.

“As I’ve always said, the most important thing to me is my law license, and I’m not going to do anything to jeopardize that,” he replied.

When Kramer reached Allinger, he angrily referred her to the union office. A spokesman there insisted the union “has a long track record of adhering to the laws governing political action and campaign finance.”

The spokesman refused to say whether the union had received a subpoena. Schaffer said he will gladly talk to prosecutors.