Finding concerted activity because "a reasonable inference can be drawn that the men involved considered that they had a grievance and decided, among themselves, that they would take it up with management"
Invalidating administrative order as "arbitrary, capricious, an abuse of discretion," see 5 U.S.C. ยง 706, because "[t]he inequity of retroactive policy making . . . is the sort of thing our system of law abhors"