An investigation is prompting a new round of questions about the relationship between the mayor's campaign cash and his policy positions. NY1's Grace Rauh has the story.

When Bill de Blasio was running for office, he promised to ban horse-drawn carriages in the first week of his administration. Critics thought it was an odd priority for a politician focused on fighting income-inequality.

"When I started out, I actually had a kind of romantic notion about the horse carriages, that they were something positive," de Blasio said September 2013. "But the more I learned, the more uncomfortable I became."

While his fight against carriages has stalled, the mayor's opposition appears to have paid off on another front: the donors behind the effort to end the industry donated $100,000 to the mayor's non-profit group.

They also bankrolled an aggressive ad campaign against de Blasio's rival in the 2013 mayor's race, Christine Quinn, which helped clear the way for de Blasio.

When NY1 asked the mayor about the investigation, first reported in the Wall Street Journal, he defended his actions and insisted he had done nothing wrong.

"We follow the law very carefully in everything we do," de Blasio said. "And I ran very clearly for office saying this is a change we had to make in our city."

But de Blasio's crusade against horse carriages is only one example where big money intersects with the mayor's agenda.

The yellow taxi industry pumped more than $500,000 into the mayor's campaign, and then spent tens of thousands more on groups tied to de Blasio.

Last summer, the mayor went hard after the industry's chief competitor, Uber.

He proposed limiting the number of for-hire vehicles on city streets. After coming under fire from Uber-riding New Yorkers and others, he backed off.

One little-noticed case is detailed in a Politico New York story, "The Transactional Mayor Returns."

The head of a company that was trying to sell the city rat-repelling trash bags donated $100,000 to the mayor's non-profit. The city subsequently bought some.