Not a lawer and this is not lawer advice, but the trick usually is to add a lawful reasson in the official communication of the strike. It worked, at least, in the 90s 2000s with a 1 hour strike against the war in Irak and more recently in the strikes in the strugle for the independence Catalonia.
Edit: oops, dates…
USA worker? /s
The US has not signed the ILO convention C095 - Protection of Wages Convention, 1949 (No. 95)