If the HudsonYardsproject continued without the casement, officials said, it would block access for any new tunnel projects looking to serve Penn Station's existing tracks.
The move is new ground for closely held Related, which recently began work on its 26-acre HudsonYardsproject in Manhattan, a mixed-used project that is the largest development in the city.
The Bloomberg administration is considering such a delay because it doesn't want to create competition for the city's ambitious HudsonYardsproject on the Far West Side, where developers are still seeking anchor tenants to help get large office towers off the ground.