Except they were generating zero revenue during the time they were closed. That is pretty close to a fine.
I do also think they should be fined for preventing a union from forming, but having them pay back wages would be more of a fine than most places would be fined because there are basically no penalties for this kind of behavior.
xkcd #2872: Hydrothermal Vents ( imgs.xkcd.com )
xkcd.com/2872/...
Starbucks told to reopen stores Labor board finds were closed over union organizing ( www.axios.com )