In close urban construction environments, such as those encountered in New York City every day, underpinning is inevitably required on many projects. Since almost every parcel of land has at least three adjoining properties (one in the rear and one on each side), the possibility exists that any given construction project could require underpinning on up to three separate parcels.
In the City of New York, it is mandatory that prior to underpinning an adjacent property the written consent of the adjoining land owner be obtained. If written consent cannot be obtained, the developer has the option of attempting to secure judicial permission to underpin the project under Real Property Actions and Proceedings Law Section 881. However, if no judicial license is obtained, and no consent exists, and you proceed to underpin the adjoining property anyway, there is a very good chance that once the New York City Department of Buildings discovers your underpinning was done without written consent, they will audit your construction project and shut you down. If construction is ongoing, a full stop work order will be issued. If construction is complete, your permit will likely still be revoked and the Department of Buildings will refuse to issue you a certificate of occupancy.
What will follow is years and tens of thousands of dollars in litigation trying to find a way around your initial mistake in not obtaining written consent. There is a significant chance, that there will not be any way around it and your project will suffer permanent incapacitation unless you can convince the adjoining land owner to provide subsequent consent which, of course, will involve you writing a check.