PHILADELPHIA (WPVI) -- A major work stoppage is affecting construction at more than 20 sites all over Philadelphia and the metro area.The International Union of Operating Engineers Local 542 that represents crane and elevator operators went on strike Monday, as their contract stalemate with the General Building Contractors Association continues.The contract expired May 1st.Among the buildings affected are the new Comcast tower, under construction now, and Children's Hospital of Philadelphia, which is in the process of an expansion.The workers who make a minimum of $42 to $46 an hour cite many issues."Our proposals are reasonable. They want to renegotiate our contract. They don't want to negotiate a future contract. They want to renegotiate, that's not why we're there," Charles Priscopo, IUOE Local 542 spokesperson, said.The union says this is their first strike in 25 years. It has workers and contractors losing big money every hour they are slowed down or shut down.The Contractors Association says all involved are losing a lot of money."We believe that people should be fairly compensated for the work they do, but at the same time, it's our responsibility, our partners in the union and the contractors' responsibility, to make sure that we continue to safeguard the market, which means staying competitive and removing wasteful items from agreements," Ben Connnors of the General Building Contractors Association said.----------