ALBANY - The state Board of Elections found that New York City Mayor Bill de Blasio and his political team committed “willful and flagrant violations” of campaign-finance laws in its efforts to oust Republican senators and referred the matter for criminal prosecution, according to an internal memo.

In a letter to the board in January, chief investigator Risa Sugarman said de Blasio conspired with a hotel union and a teachers’ union, and political consultants, to channel money in 2014 to three upstate Democratic Senate candidates and skirt campaign-finance laws. The mayor’s team directed donations to be funneled through certain political committees to mask the source and then sent the money on to the candidates — one check included the notation “donation per mayor” in the memo line.

Sugarman recommended the matter be sent to the Manhattan district attorney’s office for prosecution, saying “reasonable cause exists” to “investigate any indictable offense.”

Federal officials already are probing campaign-finance issues in the de Blasio’s 2013 mayoral campaign.