If you have not been paid by a contractor or subcontractor as agreed upon for doing a public improvement project with a mayoral New York City agency, you may file a notice of lien for the value of the labor and materials against them. When a lien has been filed, the Department of Finance (Finance) will withhold one and one half times the stated value of the lien from the City's payments to the contractor for one year. At the end of one year, the lien will expire unless it is extended by filing a Notice of Extension.
You may file a notice of lien after you have provided the labor or materials. You have 30 days from the time the project is accepted by the mayoral agency - regardless of when your work was finished - to file your Mechanic's Lien on a public project in New York City.
Authorities such as Transit, Housing, School Construction, etc. handle their own liens. You should file the appropriate documents directly with them.