It’s completely legal. They did the exact same thing during the last strike.
I hope they do strike again...I like crossing picket lines.
During the last strike, I once shopped at an Albertson's that had been targeted for a demonstration. As I exited, some of the strikers yelled at me, "Shame! Shame!" Whereupon, I waved my sales slip in their faces, and they shouted some more. I knew they wouldn't do more than yell, since there was a cop keeping watch.