The justification seems to go along the lines of "our elected government wouldn't give the workers enough rights so we had to have them imposed by an unelected body outside".
This is very dangerous logic and it assumes that EU will only ever give us desirable non-democratic impositions.
Either you accept the EU is partially non-democratic or you don't.
You can't turn a blind eye just when it does things you like.
Even though I am a firm believer in workers rights (I don't think they go anywhere like far enough actually), I oppose the idea that the EU can decide we have to do things that our government didn't want to - that way madness lies.