N.J. Stat. § 18A:16-1.1a
A vacant teaching position, or the position of a teacher who is absent for an extended time period, shall not be filled in any school year by one or more individuals holding a substitute credential issued by the State Board of Education pursuant to the provisions of N.J.S. 18A:6-38 for a total amount of time exceeding 20 school days. The commissioner may grant an extension of up to an additional 20 school days upon written application from the school district demonstrating the district's inability to hire an appropriately certified teacher for the vacant position within the original 20-day time limit. During a public health emergency declared by the Governor pursuant to the "Emergency Health Powers Act," P.L. 2005, c. 222(C.26:13-1 et seq.), a vacant or absent position may be filled by a holder of a substitute credential for up to 40 school days and for an additional 20 school days upon written application to the Commissioner of Education or the commissioner's designee, demonstrating the district's inability to hire an appropriately certified teacher within the 40-day time limit and that the individuals are periodically monitored and supported by the credential holder's supervisor.
N.J.S. § 18A:16-1.1a