A gross oversimplification, but ...

In effect the RLA is in some ways similar to our agreement to arbitrate our seniority list. It mostly does not change the law and practice as much a it changes the process of getting to a conclusion. The rules regarding Alter Ego remain largely intact. The NLRA is a more general piece of legislation geared to general and local labor situations. The NLRA covers the vast majority of American workers because only a small percentage of them work in national transportation systems. Under the NLRA, employees can unionize in small localized groups, and government led mediation is not a required step in the negotiation process.

The RLA is a dispute resolution process designed to avoid work stoppages in the critical transportation industry. Rail lines lent themselves to local monopolies since the rail line itself was a very finite resource. During a time of war, a work stoppage on a rail line could be a security threat.

Obviously the same is not true of airlines. The RLA is outdated. With our current administration the power of the RLA could be diminished.