It is up to the Union to define struck work. When NWA struck in 98, the union took a "snapshot" of the flying of the regional carriers. The regionals (Mesaba, Pinnacle(formerly Express 1)) were allowed to fly routes that the regionals were already flying, even if NWA also flew those routes. However, if the regionals tried to increase frequency (more flights)or lift (bigger equipment) then that would be considered flying struck work. Obviously one could not go on Mesaba from Detroit to L.A., so it didn't affect the regionals to a great extent, but it was closely monitored.