From FIFA Statutes, June 2019 edition
Section IV – Sporting Integrity.
9. Principles of Promotion and Relegation
A club’s entitlement to take part in a domestic league championship shall depend principally on sporting merit. A club shall qualify for a domestic league championship by remaining in a certain division or by being promoted or relegated to another at the end of a season.
In addition to qualification on sporting merit, a club’s participation in a domestic league championship may be subject to other criteria within the scope of the licensing procedure, whereby the emphasis is on sporting, infrastructural, administrative, legal and financial considerations. Licensing decisions must be able to be examined by the member association’s body of appeal.
Altering the legal form or company structure of a club to facilitate
its qualification on sporting merit and/or its receipt of a licence for a domestic league championship, to the detriment of the integrity of a sports competition, is prohibited. This includes, for example, changing the headquarters, changing the name or transferring stakeholdings between different clubs. Prohibitive decisions must be able to be examined by the member association’s body of appeal.
Each member association is responsible for deciding national issues, which may not be delegated to the leagues. Each confederation is responsible
for deciding issues involving more than one association concerning its own territory. FIFA is responsible for deciding international issues involving more than one confederation.
Interpretations of the above:
The statute is fairly clear that each national association is to have an open system of leagues, with teams moving up and down the ladder based on their on-field performance.
That said, FIFA leaves open the possibility that participation in a league may be made subject to other criteria. Such additional requirements could involve criteria such as infrastructure or financials. FIFA also makes clear that each national association must have a mechanism and a judicial body to which an appeal can be made.