Potential landmarks are first nominated to the LPC from citizens, property owners, city government staff, or commissioners or other staff of the LPC. Subsequently, the LPC conducts a survey of properties, visiting sites to determine which structures or properties should be researched further. The selected properties will then be discussed at public hearings where support or opposition to a proposed landmark designation are recorded. According to the Landmarks Preservation Law, a building must be at least thirty years old before the LPC can declare it a landmark. Approval of a landmark designation requires six commissioners to vote in favor. Approved designations are then sent to the New York City Council, which receives reports from other city agencies including the New York City Planning Commission, and decides whether to confirm, modify, or veto the designation. Before 1990, the New York City Board of Estimate held veto power, rather than the City Council. After the City Council's final approval, a landmark designation may be overturned if an appeal is filed within 90 days.