Liberty Property Trust hoped to get the One Pennsylvania Plaza site designated a Keystone Opportunity Improvement Zone (KOZ). KOZ designation was intended to encourage development in poor, blighted areas by exempting the tenants of the building from all state and local taxes. Designating One Pennsylvania Plaza a KOZ was supported by then Pennsylvania Governor Ed Rendell, who said it was important to keep corporations within the city. At the time, many of Philadelphia's big employers' leases, including Comcast's, were due to expire, and the employers were considering the possibility of moving out of the city and state. Rendell also said allowing Comcast to enlarge its headquarters by moving into One Pennsylvania Plaza could attract other corporate headquarters to the city. However, other Center City building owners, including Comcast's landlord at Centre Square, HRPT Properties Trust, were opposed to the plan. They said giving the tower the KOZ designation would give it an unfair advantage because Liberty Property Trust could charge above-market rents since the tax breaks would offset the cost for tenants. The group believed tenants attracted to One Pennsylvania Plaza because of the tax breaks would cause more vacancies in other Center City skyscrapers, rather than attracting more business to blighted areas as intended under the law. In early 2004, Center City had a vacancy rate of 12.8%.