You would have to examine your condominium’s declaration, by-laws and rules and regulations to see if there is a clause specific to large events being held in units. If nothing is stipulated, I think a board would be overstepping their boundaries by requiring board approval. However, the board pursuant to its general authority to manage the condominium and its common areas, may want to acknowledge, via letter, that they are aware of such a gathering being planned and remind the owner of their responsibility for their guests (e.g. noise by-laws, building damage, garbage removal, elevator use etc.).

The prevailing factor with respect to the amount of guests permitted would be the C of O (Certificate of Occupany) for the unit, the elevator and the common party room, if your building has one. The C of O would stipulate the maximum amount of people allowed in any of the areas. While Ned's advisement to review your By-laws and House Rules is correct, a review of the C of O is necessary to ensure safety and Fire Department requirements are being complied with, and if the board determines such was not the case, and the number of guests exceeded the maximum allowable occupancy, the board must then notify the unit owner of the violation and be clear the condition cannot be repeated during their next event.