An investigation by the New York State Board of Elections found evidence of flagrant violations of campaign finance law by a team of people that Mayor Bill de Blasio created to raise money for Democrats running for the State Senate in 2014, according to a confidential board report.

The board sent the report to Cyrus R. Vance Jr., the Manhattan district attorney, three months ago, prompting a criminal investigation into the fund-raising.

The mayor’s Senate effort, which failed in its goal to wrest the legislative body from Republican control, has proved damaging to him in multiple ways. Democrats remained in the minority in the Senate; the mayor’s relationship with Senate Republicans was severely strained, hurting his ability to win support in Albany for his agenda; and now it has led to one of several investigations that are tarnishing his administration.

The investigation by the state board was reported on Friday by The Daily News.

The board’s investigation, and the subsequent continuing inquiry by Manhattan prosecutors, is looking at whether there was an effort to illegally circumvent limits on campaign contributions to individual candidates by directing money instead through Democratic Party county committees and a statewide party campaign committee.