You're not giving the situation leading up to the eviction threat, so my answer will be necessarily vague.
I believe it's the same situation as a non-regulated renter with a lease, who is accused by the landlord of violating the lease. The board has to file an eviction suit in housing court, and has to convince a judge that you somehow violated your proprietary lease to the apartment. Without knowing the situation, the building bylaws, proprietary lease, and house rules, I can't give you too much more.