N.J. Stat. Ann. § 48:4-13

Any owner desiring to be exempt from obtaining or filing such insurance policy, as aforesaid, shall make application to the Commissioner of Banking and Insurance, showing its financial ability to pay such damages, whereupon the commissioner, if reasonably satisfied of the applicant's financial ability, shall by written order make such exemption. The commissioner may from time to time require further statements of the financial ability of such company; and if at any time, in the opinion of the commissioner, such company appears no longer able to pay damages, the commissioner shall revoke his order granting exemption, in which case the said company shall immediately insure its liability as required by law.