New Jersey Statutes Title 54. Taxation 54 § 5-100

In an action in the Superior Court to foreclose the right of any defendant therein named to redeem lands from the lien of a certificate of sale thereof issued for nonpayment of taxes or other municipal lien, the validity of the tax or other municipal lien for which the sale was made and certificate issued, and the validity of the proceedings to sell the lands shall be conclusively presumed unless a defendant in the action shall set up as a defense thereto the invalidity of the tax or other municipal lien or the invalidity of the proceedings to sell or the invalidity of the sale. All questions as to such invalidity may be tried in the action.