EFL rules - (Section 3) Rule 11.1
11
Replacement of Clubs Ceasing to be Members
11.1
Admission of new Clubs. For so long as the number of Clubs in The League shall be 72 or more no new club shall be admitted as a member of The League to replace a Club ceasing to be a member. In the event of the number of Clubs falling to below 72 the Board shall be empowered to admit clubs as new members up to a maximum number of 72 Clubs. Such new members shall only be admitted prior to the beginning of a Season, and shall play in League Two in their first Season.
https://www.efl.com/-more/governance...---the-league/
Edit - Seems to suggest the EFL would protect its members by reducing the number of relegations.