CCW or HR218CCW on interstate bus travel?

Maybe a knowledgeable TSA person can answer this question by citing an actual CFR section: Is there a Federal Law that prohibits an individual - either a properly licensed civilian or an LEO carrying pursuant to HR218 - from carrying a concealed weapon on an interstate bus trip? I have heard that Greyhound prohibits CCW on their buses, but is it policy, or something actually enforceable by Federal law?

Pretty sure that it's Greyhound policy.

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