This is the key passage. That may be true at some point, but it isn't now:
> The filing also disputed SpaceX’s argument that it is a “carrier by air transporting mail for or under contract with the United States Government.” Evidence presented by SpaceX shows only that it carried SpaceX employee letters to the crew of the International Space Station and “crew supplies provided for by the US government in its contracts with SpaceX to haul cargo to the ISS,” the filing said. “They do not show that the government has contracted with SpaceX as a ‘mail carrier.’”
> SpaceX’s argument “is rife with speculation regarding its plans for the future,” the ex-employees’ attorneys told the NMB. “One can only surmise that the reason for its constant reference to its future intent to develop its role as a ‘common carrier’ is the lack of current standing in that capacity.” The filing said Congress would have to add space travel to the Railway Labor Act’s jurisdiction in order for SpaceX to be considered a common carrier.
> The filing also disputed SpaceX’s argument that it is a “carrier by air transporting mail for or under contract with the United States Government.” Evidence presented by SpaceX shows only that it carried SpaceX employee letters to the crew of the International Space Station and “crew supplies provided for by the US government in its contracts with SpaceX to haul cargo to the ISS,” the filing said. “They do not show that the government has contracted with SpaceX as a ‘mail carrier.’”
> SpaceX’s argument “is rife with speculation regarding its plans for the future,” the ex-employees’ attorneys told the NMB. “One can only surmise that the reason for its constant reference to its future intent to develop its role as a ‘common carrier’ is the lack of current standing in that capacity.” The filing said Congress would have to add space travel to the Railway Labor Act’s jurisdiction in order for SpaceX to be considered a common carrier.