I should mention that
Tum v. Barber Foods, which was consolidated for oral argument together with
IBP, Inc. v. Alvarez, concerns a practically identical issue (and outcome, on the part of the 1st Circuit), except at a chicken plant in Maine, rather than a cow plant in Washington.
Barber Foods' business is also not as violent as IBP's, since it only transforms boneless chicken breasts into "stuffed entrees, chicken fingers, and nuggets."
I also had a look at the government's brief filed in support of the employees at the IBP plant, which fairly eviscerates all of IBP's legal positions, to the point of making them appear frivolous.
Speaking of chickens.