New condo association board gets elected by cheating and tampering

We had an election of condo board officers this week. The incumbents won by a stupendously large margin, which we know was done by interfering with the locked ballot box that contained mail-in ballots. Our condo association by-laws say that elections are to be done at a meeting or with a proxy, nothing about mail-in ballots. This condo board, however, sent out mail-in ballots to all 1500 units in our 55+ condo association in NY. They ignore the by-laws by having a mail-in ballot instead of a proxy so it is easier for them to cheat. Then they sent people to visit older residents and shut-ins offering to "help them fill out their ballots." 35% of the votes took place on election day, using an official election machine, and 65% mail-in ballots were opened and counted on election day. According to the machine votes, one incumbent and 3 new people were clearly elected. However, when the mail-in ballots were counted, low and behold, an overwhelming number of votes went to the four incumbents. I know they cheated and tampered with the mail-in votes, but it will be hard to prove. Never in the history of this place have there been so many votes. What recourse do we have?