New York Consolidated Laws, Local Finance Law - LFN § 80.00 Bond resolution, or note resolution or certificate, may contain estoppel clause

1. Such obligations are authorized for an object or purpose for which the municipality, school district or district corporation is not authorized to expend money, or

2. The provisions of law which should be complied with at the date of the publication of such resolution or summary thereof, or certificate, as the case may be, are not substantially complied with, and an action, suit or proceeding contesting such validity, is commenced within twenty days after the date of such publication, or

3. Such obligations are authorized in violation of the provisions of the constitution.